Wind blowing (whoosh) like noise at right front from inside
 

Drove the car in the morning with no problem. Parked under the sun for a few hours. When I drove it in the afternoon, I heard a wind blowing (whoosh) like noise inside the car from the right (passenger) front side. The noise is apparently there when the A/C is on. But it is not as apparent, or not there when the A/C is off. The noise is most audible when engine runs between 1400 and 2000 rpm, whether at standstill or moving. I don't hear anything from the engine bay when the hood is hung up. What is right beyond the right dash (or between the dash and firewall) that may produce such a noise?

Car is a 2004 3.0L Quattro.

Open your hood, then peel the rubber strip off the front of the piece of plastic in front of the windshield (it is press-fit on and you will be reusing it, so don't damage it), then lift the plastic piece in front of the windshield. If you look down towards the corner of the passenger's side, you'll see the blower motor. You may have to remove the cabin air filter to see it (it's a square charcoal filter) make sure that is clean and there is not water, etc. in this area. There may be living creatures in there, so a glove could be handy....

I'm not 100% sure this is it, and I haven't heard it make the exact noise you are referring to - but it's my first guess.

My second guess may be the mixing door but I'm unsure of this and cleaning the blower motor is a good idea either way.

I will take a look there the coming weekend. However, as the noise comes only when the A/C compressor is on, and depends on the engine RPM, it comes to my mind that the noise may come from the A/C expansion valve that is also supposed to be located there(I suppose the A/C compressor is driven by the engine). I will be probably be able to locate the source when I am there. As the A/C works just fine, I am not truly worrying. Thanks.