About two weeks ago I started to notice that when I turn on my a/c there is a loud thump. It's not a horrible sound but annoying none the less. Any ideas whats causing it?If this is a big sign of a big problem I just wanna start as soon as I can.

 

Is it inside the car or out? Does it happen repeatedly or not? Have you noticed a change in the a/c temperature? A little more information would help, but taking a shot in the dark, your having some kind of belt slippage.

 

It seems to be just on the other side of the dash, closest to the engine. And it seems to only happen when I turn the a/c on right afteri first start the car, and it just happens once.If I turn the air on after Ive been driving it doesnt usually do it. And theres no change in temperature or anything like that.

 

If it was an old car then then i'd say it was the vacuum pulling the air door shut but on our cars the only thing I can think of that would possibly make a thunk sound would be the compressor clutch lost it's bushings. But, that's more of a off/on clicking sound.