Air conditioning whistles really loud!!!

So that I don’t have anything to do I want to bother you again. My air conditioner actually works quite reasonably only happens whenever I stop or stand that it starts to whistle/ howl/jaul. I think it also comes direction front passenger area, behind the cockpit. If I turn off the climate then it doesn’t immediately wave, sounds like pressure is dropped like a lock, is really annoying. Sometimes it just happens during the ride. from the blower stage. Achso is a manual one and was refilled two years ago, also have no fluid loss I know that I can not do it myself anyway, but would like to give the VW man a tip so that the not 2 Studen is looking for at now 80 € hourly wage. Can this be any bearing or fan bulge????? For 1000 € repair costs I like to listen to this for 3 years!!!!!