AC compressor noise?

I have been hearing a whining sound that increases and decreases with engine speed. My first thought was a tranny pump whine but when the AC is off it doesn't whine so guess it is the AC compressor. At idle with the hood up and the AC cycling the noise seems louder than normal.
Could this just be the clutch? Anyone else have this happen. AC works great. Truck has 56K miles.
Thanks...

 

take the belt of and spin each pulley by hand could be another pulley getting loaded up when a/c is on

 

Thanks

 

I recently rebuilt my AC system and my new UAC compressor does what you describe. It's kind of a howl/wine/moan that is most noticeable at low idle. Been doing it for a couple months now and doesn't seem to be causing a problem. It was annoying at first, but I just turned the radio up. I probably wouldn't buy a UAC compressor again though.

 

Spot on Bro, the idler pulley next to the alternator wobbles.
Thanks

 

cool glad i could help.