So I'm pretty sure the bearings are going out in my a/c compressor (makes a slight whirring/light grinding noise) but what I don't understand is why does it only make noise when the a/c is off?

As soon as I turn a/c on the air blows cold and the noise goes away! belt is on snug and a/c has correct charge levels... Weeird...

Any thoughts? Thanks.

 

Nudge.

 

It's a slight grinding noise, but loud.

 

The AC compressor clutch is probably going out. When the AC isn't on the pulley's spinning across the clutch and not actuating the compressor so as to reduce drag on the engine. When you turn the compressor on, the clutch and compressor are engaged and the unit spins as one.

Replace your compressor if you're really concerned about it. If not, turn up your music.