Rattling Noise With A/C On — Goes Away When Turned Off

[Cegla]

Hi everyone,

Has anyone experienced a sound like this with the A/C on? Here’s the video:



It’s exactly what I’m hearing: a sort of chirping or rattling noise that increases with engine RPM and disappears completely the moment I turn the A/C off.

This is happening on my Audi, but I’d love to hear from anyone who’s had a similar issue, regardless of brand. If you’ve come across something like this and managed to find the cause or a fix, I’d really appreciate your input.

Thanks in advance!

 

[Rhymingmechanic]

Does this car have a separate A/C tensioner? A bad tensioner caused an A/C rattle on my Chevy pickup.

That's just a wild guess. I couldn't hear much other than interior noises in the video.

 

[JavierH19]

Tensioner is always spinning when the engine runs so maybe the compressor is failing and if that's the case change it now before you end up needing to change the condenser and need to flush the metal out of the system. I don't imagine these have a fot and a screen you can inspect but I don't know for sure.

 

[Mcbeem5]

My 15 year old silverado AC started getting noisy,ran it all summer, compressor failed in september. I had run across this info on AC,so I figured it was running on borrowed time!

Even if a compressor is still turning, it may have to be replaced if it is leaking, making excessive noise or not working correctly. Some compressors are naturally noisier than others, but loud knocking noises can sometimes be caused by air in the system (the cure here is to vacuum purge the system to remove the unwanted air, then to recharge the system with refrigerant). Metallic noises and bearing noise are usually signals that the compressor is about to fail.

 

[zzyzzx]

I am also thinking that you need a new AC compressor.

 

[D60]

The video being taken from the passenger compartment doesn't help us know if this is the compressor under the hood or some oddity of the HVAC in the dash. I'd be inclined to think the latter given the POV

The compressor on my '11 SuperDuty 6.2 sounds a bit like a chirping box of rocks when engaged but it's been like that for years. I can't really hear it from the cabin but it's noticeable standing at the grille.

Basically, a modicum of effort is required before posing this question. Is the noise only inside? Is it louder under the hood? Not present under the hood?

 

[Dborch41]

I'm a big fan of mechanic's stethoscopes, I got a cheapo one from the parts store and it works just fine for troubleshooting unusual noises like this. Touch the probe to the compressor right behind the clutch and have someone turn the A/C on, the noise will be obvious. Just be careful around all the spinny bits.

 

[Mechanician]

You can also use a Loooonnnng screwdriver to listen (if you already have one) by holding the handle against your ear, and touching the tip to whichever part you suspect.

 

[daniel327]

I had a very similar problem on my Toyota 2AR-FE engine. Using a stethoscope it would have been easy to conclude that it was the AC compressor clutch, the coolant pump, the alternator, or the serpentine belt tensioner. However, the problem was resolved when I replaced the rubber bushing in the engine's balance shaft coupling.

 

[D60]

I'm a fan of the old plastic jug on a broomstick