Vibrating sound when AC is on. What is it?

[Ocean View]

My Indy installed a new AC Compressor/drier and now it makes a weird rubbing/vibrating sound when the AC is on.
My car has never made this sound before and it feels like the engine is loosing some of its power when it is on.
Could it be that the belt is on too tight?
The sound is not constant and varies depending on the speed of the car/engine.
I noticed it mostly when the car is going about 20-25mph (2,000 rpm)
It also is barely noticeable when the car is idling.
The sound is not noticeable under the hood but only in the car.

I am going to take the car back tomorrow but I wanted to get some ideas as to what it is before I go.

Any ideas?

BTW, the indy used a new OEM compressor.