Homer1946

It appears to be fixed. No noise so far. They replace some subset of fans and door servos, the compressor, and finally the high side compressor hose which seems to have fixed it.

The technician still thinks he can barley hear the noise if he listens with an electronic ear so Audi is having me bring the car back next week to replace the expansion valve.

All I did was ask about the noise. I didn't eve make a big deal about it.

Lenny Lim

i got a call from my authorised agent today. it seems Audi has responded and suggested a fix for this train sound/whistling noise. Agent has ordered a new a/c compressor and now awaiting for the part to arrive.
I will share again if the change in the a/c compressor will eventually fix this problem.

Homer1946

The final outcome (maybe).

After three weeks and multiple part replacements including various servos and fans related to the AC and the compressor, they replaced the low side hose (not the the high side hose) and the expansion valve which seem to have mostly eliminated the noise. I have only heard it once since getting the car back (around a week) and it was much much fainter. The noise used to be very frequent and much louder.

However the fact that the temperature (in Texas) has changed significantly since I dropped off the car chaning how the climate controls operates is a confounding factor. The dealer is clearly ready to continue the fight if the problem returns (and I complain about it).

As an aside. I had two different loander S4's during this. The first had the stock radio but the second had the B&O upgrade, and upgrade which is the same price as the Bose in my car. However the B&O in the S4 was dramitically better. So whereas before I was happy with my radio, not I think it sucks....Damned loaner.

petersaudi

I was wondering if this was the final fix for AC train siren noise

gogo_vs

I am not sure if this relates to the same noise but I can hear it even when the AC unit is completely off.

petersaudi

my car is presently at dealer for this problem. It only happens with air on and
you can hear it more when slowing down or coming to a stop.

I was able to duplicate the sound for dealership mechanic but they have no
idea what could be causing it..
If anybody knows the fix please post.

car is 2014 a6

KevinDaytona

I think I was one of two original people on the forum that had this problem and still have the issue on mine they have not been able to fix it. Around 80,000 miles on mine now and its worse than ever. But no fix. Lots of parts replaced though.

Footfury

Did they ever figure out what is causing this in the 2014? I have the same issue. The mechanic tried to say it's normal but couldn't show me another 2014 that's making the whistle when the a/c is on.

Mrchntmarine

So we're 2 or 3 months with the new car and this whistling / humming noise is driving me nuts. Is anyone else experiencing this???? Happening when the ac is on.....

snagitseven

Did you read the thread? Several have had the issue and there is apparently a fix according to the recent posts.