Your AC was running silently for years. Then one day it starts rattling, buzzing, hissing, or making a grinding sound you have never heard before. In Kolkata's summer — when you cannot afford to switch it off — this is alarming.
Here is the good news: every type of AC noise has a specific cause. If you know what the sound is, you know what the problem is — and whether it is something you can address yourself or something that needs a technician today.
⚠ Important: Some AC noises — particularly hissing, burning smells, or loud banging — require you to switch the AC off immediately. Do not keep running a noisy AC without understanding the cause. In several cases, continuing to run it causes damage that costs ₹6,000 to ₹18,000 to repair.
We are
Unique Aircon — certified AC repair specialists based in Jadavpur, serving South and Central Kolkata for 9+ years. For same-day noise diagnosis and repair, call
+91 83469 04100 or
WhatsApp us.
Quick Noise Diagnosis — Find Your Sound
Find the sound your AC is making below and jump straight to the cause and fix:
| Sound |
Most Likely Cause |
Urgency |
DIY? |
| Rattling |
Loose panel, debris in fan, loose screws |
Moderate |
Partly |
| Buzzing |
Electrical fault, failing capacitor, loose wiring |
High |
No |
| Hissing |
Refrigerant gas leak |
Switch off now |
No |
| Banging / Clanking |
Loose or broken internal part, compressor issue |
Switch off now |
No |
| Squealing / Screeching |
Worn fan motor bearings, belt issue |
High |
No |
| Clicking |
Debris in fan, electrical relay fault, thermostat |
Moderate |
No |
| Gurgling / Bubbling |
Refrigerant leak or blocked drain pipe |
High |
No |
| Whistling |
Blocked filter, airflow restriction |
Low |
Yes |
AC Noise Causes — Detailed Guide for Kolkata Homes
🔩
Rattling Sound from AC
From indoor unit, outdoor unit, or both
MODERATE
Rattling is the most common AC noise in Kolkata homes — and often the least serious. It usually means something is loose. Over time, constant vibration from the compressor and fan motors loosens screws, panels, and brackets. In Kolkata, the problem worsens during monsoon when wooden wall brackets swell and shrink with moisture changes.
Common causes:
- Loose front panel or cover on the indoor unit
- Debris — leaves, dust clumps, insects — inside the outdoor unit fan
- Loose screws on the indoor unit mounting bracket
- Outdoor unit vibrating against a loose wall bracket or balcony floor
- Loose copper pipe rattling against the wall
DIY check first: Press gently on the front panel of the indoor unit while it is running — if the rattling stops, the panel just needs its clips tightened. For the outdoor unit, switch it off at the breaker and look inside for any visible leaves or debris caught in the fan blades.
Call a technician if: The rattling is coming from inside the unit (not the cover), is getting louder over days, or is accompanied by vibration strong enough to feel in the wall.
⚡
Buzzing Sound from AC
Usually from outdoor unit or indoor unit PCB
HIGH URGENCY
A buzzing sound — especially from the outdoor unit — is a serious warning in Kolkata homes. The most common cause is an electrical issue: a failing capacitor, loose or corroded wiring, or a contactor wearing out. In South Kolkata where voltage fluctuations are frequent during peak summer, electrical components face repeated stress that accelerates this kind of failure.
Common causes in Kolkata specifically:
- Failing start or run capacitor — very common after Kolkata's long 7-month season
- Loose or corroded electrical connections from voltage fluctuation damage
- Worn contactor in the outdoor unit
- Compressor struggling to start — indicates compressor weakness
- Outdoor fan motor bearing failing
Do not ignore buzzing. A failing capacitor that is not replaced will eventually prevent the AC from starting at all — leaving you without cooling in peak summer. Capacitor replacement in Kolkata costs ₹500 to ₹1,200 — far less than a compressor repair that results from running with a weak capacitor for months.
Action: Call a technician. Do not attempt to open the outdoor unit yourself — capacitors store charge and can cause serious electrical shock even when the unit is switched off.
💨
Hissing Sound from AC
From pipes, indoor unit, or outdoor unit
SWITCH OFF NOW
A hissing sound is one of the most serious noises an AC can make. It almost always indicates refrigerant gas leaking from the system — through a cracked pipe joint, a valve failure, or a corroded connection point. As the pressurised gas escapes, it creates the hissing sound you hear.
In Kolkata, refrigerant leaks develop most commonly at pipe joints that have been subjected to repeated thermal expansion and contraction over many summers, and at outdoor unit connections that have corroded in the monsoon humidity.
Switch off the AC immediately at the main breaker — not just the remote. Running an AC with a refrigerant leak forces the compressor to work against incorrect pressure, causing overheating and failure within hours to days. Compressor replacement costs ₹6,000 to ₹18,000. The gas leak repair itself costs ₹500 to ₹2,000.
What happens next: A technician uses a leak detector or soapy water test to find the exact leak point, repairs the pipe or joint, and then refills the refrigerant to correct pressure. Read our
AC gas charging cost guide to understand the full repair cost.
💥
Banging or Clanking Sound
Usually from outdoor unit compressor or fan
SWITCH OFF NOW
Loud banging or clanking — especially from the outdoor unit — means something has broken or come completely loose inside the unit. The most common causes are a broken compressor piston, a fan blade that has snapped and is hitting the casing, or a connecting rod that has failed inside the compressor.
Switch off immediately. A broken fan blade spinning inside the casing can cause catastrophic damage to surrounding components within minutes. Do not restart the AC. Call a technician the same day — this is not a noise you can monitor and wait on.
Repair cost in Kolkata: Fan blade replacement ₹800 to ₹2,000. Compressor repair or replacement ₹6,000 to ₹18,000 depending on brand and tonnage. Early diagnosis keeps costs lower — continuing to run causes more parts to fail.
😬
Squealing or Screeching Sound
From fan motor in indoor or outdoor unit
HIGH URGENCY
A high-pitched squealing or screeching sound — especially on startup or when the AC runs at high fan speed — points to fan motor bearings that are worn dry and failing. In Kolkata's humid climate, motor bearings corrode faster than in drier cities, particularly in outdoor units that face months of monsoon exposure every year.
- Indoor unit fan motor bearings worn or dry
- Outdoor condenser fan motor failing
- Blower wheel rubbing against the housing
Action: Switch off and call a technician. Fan motor replacement in Kolkata costs ₹1,500 to ₹4,000 depending on the unit. If ignored, the motor seizes completely — the AC stops working entirely and the repair cost increases significantly.
🖱️
Clicking Sound from AC
On startup, shutdown, or continuously
MODERATE
A single click when the AC turns on or off is completely normal — it is the thermostat relay switching. However, repeated clicking throughout operation, or clicking when the AC fails to start, points to a fault.
What the clicking means:
- Continuous clicking while running: Small debris caught in the blower fan hitting on each rotation — switch off and check the indoor unit
- Clicking on startup but AC does not start: Failing capacitor or stuck compressor — needs a technician
- Clicking with remote but nothing happens: PCB or thermostat fault — replace remote batteries first, then call if it persists
DIY first: Replace remote batteries. Check if any visible debris is stuck in the indoor unit air outlet. If clicking persists, call a technician — capacitor replacement costs ₹500 to ₹1,200 and is a quick fix when caught early.
💧
Gurgling or Bubbling Sound
From indoor unit drain area or pipes
HIGH URGENCY
A gurgling or bubbling sound from the indoor unit is very common in Kolkata — particularly during and after monsoon — and has two main causes. The first is a partially blocked drain pipe where water is backed up and gurgling as air tries to pass through. The second, more serious cause is refrigerant bubbling through a leak point in the system.
If water is also dripping inside the room: The cause is almost certainly a blocked drain pipe. Flush it as described in our
AC water leaking guide. If the gurgling is without water leakage, it may be refrigerant — call a technician.
Drain pipe unblocking costs ₹300 to ₹500 at Unique Aircon and takes 20 to 30 minutes. Do this before monsoon every year to prevent the problem entirely.
🌬️
Whistling Sound from AC
From indoor unit air outlet or return air gap
LOW — DIY FIX
A high-pitched whistling from the indoor unit almost always means the air filter is severely blocked — air is being forced through tiny gaps in the clogged filter, creating the whistle sound. This is the most fixable noise on the list and the only one you can usually solve yourself in 10 minutes.
DIY fix: Open the front panel, remove the filter, rinse under running water, dry completely, and reinstall. The whistling should stop immediately. If it continues after a clean filter, the issue may be an air return gap or duct restriction — call a technician to check.
Why ACs Make More Noise in Kolkata — 3 Local Factors
1
Voltage fluctuations stress electrical components continuously. South Kolkata's grid voltage swings during peak summer load hours put repeated stress on capacitors, contactors, and motor windings. These components develop faults much faster than in cities with stable grid voltage — leading to buzzing and clicking noises earlier in the AC's life.
2
Monsoon humidity corrodes outdoor unit components. Fan motor bearings, electrical connections, and pipe joints in outdoor units face 4 to 5 months of high humidity and direct rain every year. This accelerates corrosion-based failures — squealing from corroded bearings and buzzing from corroded connections are both significantly more common in Kolkata than in drier cities.
3
7-month cooling season means 75% more annual wear. A Kolkata AC runs roughly 1,700 to 2,000 hours per year. An AC in Pune or Bangalore runs 700 to 900 hours. All moving parts — fan motors, compressor, bearings, contactors — reach their wear threshold significantly earlier in Kolkata. Noises that appear after 5 to 6 years in other cities may appear after 3 to 4 years in Kolkata homes.
AC Noise Repair Costs in Kolkata — 2026
| Noise / Problem |
Typical Repair |
Cost in Kolkata |
| Rattling — loose panel / screws |
Tighten and secure panels |
Free – ₹400 |
| Whistling — blocked filter |
Filter wash |
Free (DIY) |
| Gurgling — blocked drain pipe |
Drain pipe flush |
₹300 – ₹500 |
| Clicking — capacitor fault |
Capacitor replacement |
₹500 – ₹1,200 |
| Buzzing — electrical / contactor |
Wiring check + contactor replacement |
₹800 – ₹2,500 |
| Hissing — gas leak + refill |
Leak repair + gas recharge |
₹1,500 – ₹4,500 |
| Squealing — fan motor bearing |
Motor lubrication or replacement |
₹1,500 – ₹4,000 |
| Banging — compressor / fan blade |
Compressor or fan blade replacement |
₹2,000 – ₹18,000 |
Frequently Asked Questions
Q
My AC makes noise only when it starts — is that normal?
A single soft click on startup is completely normal — it is the thermostat relay activating. A loud thud, bang, or rattle on startup is not normal and usually indicates a compressor starting under difficulty (weak capacitor) or a loose component that rattles when vibration begins. If it is more than a soft click, have it checked.
Q
Can I keep using a noisy AC until the technician comes?
Depends on the noise. Whistling and mild rattling — yes, you can continue using it for a day or two. Hissing, banging, or loud buzzing — switch off immediately and do not restart. Running an AC with a gas leak or broken internal component causes rapidly escalating damage that turns a ₹2,000 repair into a ₹12,000 compressor replacement.
Q
My AC started making noise after monsoon — why?
Very common in Kolkata. After monsoon, two things typically happen: drain pipes get blocked with algae (causing gurgling), and outdoor unit components that were exposed to months of rain develop corrosion-related faults (causing buzzing or rattling). A post-monsoon service visit in October or November catches and fixes both before the next season begins.
Q
How quickly can you come to diagnose AC noise in Kolkata?
Based in Jadavpur, we offer same-day visits across South and Central Kolkata for noise diagnosis. Call or WhatsApp before noon for a same-day afternoon slot. We carry the most common replacement parts — capacitors, contactors, fan motors — so most noise repairs are completed in a single visit.
AC Making a Strange Noise? Get It Diagnosed Today.
Same-day diagnosis and repair across South & Central Kolkata. We carry common parts — most noise repairs completed in one visit.
📍 3/87 C. R. Colony, Jadavpur, Kolkata – 700032
Jadavpur · Garia · Tollygunge · Ballygunge · Kasba · Santoshpur · Behala · Dhakuria · Mukundapur · Ruby · Sonarpur · Bhawanipore
Last updated: June 2026 · Written by the Unique Aircon technical team, Kolkata
