W126 AC wheezing

Strange I know but today with the ac set to 20c I turned the stereo all the way down and could hear the ac wheezing. Almost sounded like someone breathing in and out. Also the sound seemed to get louder as I accelerated. There didn't appear to be any pattern to the timing of the sound. I have had the car in for an ac inspection about a week earlier and they said everything was fine and just blew threw an anti bacterial spray. Appreciate anyones thoughts on this, this is definitely a new sound that has developed over the last few days.

Matt.

[engatwork]

My initial thought is a vacuum system or damper actuator problem. Try to "feel" a difference in air flow from one of the vent discharge. Put your hand over them one at a time and see if you can "feel" the air flow speeding up or slowing down in time to the sound.

I am about to take a 1500 mile road trip so I will get my passenger to check the vents when I hear the sound again. I will report back with my findings.

Cheers
Matt.