MiX

First this noise only comes when i have the A/C on and i am moving. If i turn on the car and then turn the a/c on it does not do it. Only after i start driving. But it will continue to do it if i am driving and then come to a stop. It also not constant happens all the time but not continuous. I am thinking it might be the alternator belt b/c the a/c draws alot of power and then making the alternator work harder. Or Could the actual compressor being doing it, but then again its not constant. I tighted all belts pretty tight. Maybe i need to make them more tight or just replace them. Please help.