I own a 2002 A6 with 93,000 miles. I had the timing belt service done by my local dealer at 90,000 miles and it came back from them with a low pitch squealing sound at 1500 rpms when the A/C is on. No sound when the A/C is off. I have had it back to the dealer several times in the last 2 weeks and the tech claims that it's normal. It was not there before the service on the timing belt. The service manager took a ride with me and he admits it should not be there and changed the belt again thinking that the new serpentine belt was the cause. He claims the pulley on the compressor has nothing to do with it. The sound has not gone away and the service manager said to drive it for a 1000 miles or so and see if the belt breaks-in and the sound disappears. As of now with 3000 miles on the new belt it still is there and very annoying.

Any idea what it might by? I thought I read somewhere (but can't find it) that it had something to do with the pulley. Any help would be appreciated.

 

I have the same problem. I just got my A/C compressor changed, and ever since I got it back, it has been making the same noise. Does it get louder when you turn up the A/C fan speed? Mine is noticibly loud and I don't know what it's caused by, since I didn't change a belt of any sort.

 

Try loose belt....