98 C230 2.3 AC Problem? Belt Tensioner?

[W124300E]

Another problem needs diognosis. I hear a knocking metal like clunking noise from the AC area. I think that my Clutch/Pulley on the AC Compressor is making the noise but not 100% certain. If I take it the the stealership they will charge me $200 just to diagnose it or just buy an ac Compressor with a clutch for 289 and install it myself. BUT... I read many forums that it could be the Belt Tensioner? How can I be certain? The AC pulley has a very minimal play when I move it back and forth, could this be the problem? ITs blowing super cold air. When I turn on heat everything is fine. As soon as I turn the AC on, clutch starts spinning and then I hear the clunking/metallic sounds. It happens even more when I turn the wheel all the way to the left or right. Help Please! Thank you. Just bough car 5 days ago.