JJD

Noticed recently that there is a 'wheezing' noise when I turn my air con on. This is particularly noticeable when in using first and second gear. At first I though it was the gear box (sounds like the noise you get when car in reverse gear and moving). Thankfully the noise disappears immediately I switch air con off. It does not make this noise when car out of gear and stationary and with the engine being revved up. Hence I have ruled out compressor bearings. Has anybody else experienced problem and know how to fix it. I also notice the efficiency of the air con has dropped off as well which might have something to do with it. Any ideas.