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Hi Guys, new to this forum. I've had my A5 for nearly a year now and I'm very sure it never used to be this loud outside of the car when my AC is on. I noticed recently that when I have my windows down, if the ac is on I can hear a loud humming noise from the engine bay (no matter how high the fan speed is selected). If I've left the engine on/ac whilst popping into the shop its very noticeable. Could anyone tell me if this is normal and I've just never noticed it before or is there an issue (I assume there is). I've attatched a video to try to show the problem. Please feel free to ask for more info. Thanks

Here is a URL to a video I made so you can here it for yourselves:
 

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I think the bearing of something (compressor) is worn out and grinding up.

After making sure it's A/C, and not the alternator, roller, or the tensioner, I would get that replaced ASAP.

If replacing compressor, I recommend a brand new one. Replace the dryer as well. Also, if this has gone on for a while now, I recommend flushing the lines and condenser. If the compressor is grinding up metal, it will clogg up the lines.
 

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I am almost sure that what you're hearing has something to do with a worn-out bearing. And, if you notice it only when the AC Compressor is on then chances are it is the compressor's bearing.

Good advice from findalex above.
 

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I am having the same issue. ( the sound in the video is exactly the same as mine ) I only noticed it the last couple of days during our heat wave. The sound is the condenser fan spinning . Do the B9s only have the single fan ? I tried to have a look for a smaller aux fan but didn't see one.

In my case, it seems to quiet down after a few minutes.
 

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Just sounds like the air conditioning condenser fan behind the radiator spinning to fan to me, unless i am missing something. Mine sounds the same
 

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My B9 is similar when AC is working hard too. Very noisy outside the car. But quiet down after a couple of mins.


Sent from my iPhone using Tapatalk Pro
 

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In my experience it should not be that loud, no way. In warmer countries where A/C is used most of the time like Italy, my cars have never sounded so loud even when working very hard. In my opinion you need to work thro the various bits that it could be and eliminate them one by one to find the culprit, probably either the AC compressor or the alternator but could be both, could also be that the big aux belt needs changing.
 
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