2004 a/c compressor noise

My 2004 Aveo sedan (101,000 miles) has a noise problem with the A/C compressor, at idle and mostly when the engine is cold. When I turn on the A/C, it blows cold like air it should, but the compressor is very noisy, like bearing going out. I replaced alternator and serpentine belt tensioner and recently had Chevrolet replace the timing belt. Whenever I'm running it at highway speeds, I can't hear any noise. It's noisy only at lower speeds like 25mph or less and at idle. Whenever the a/c is off and at idle, I can just barely hear compressor noise.

My question is whether it is possible to change the bearings on the compressor without discharging the system? If I have to have my mechanic discharge the system, I'll go ahead and have a new compressor and dryer put on, but the compressor alone will be in the neighborhood of $400 for new one (not rebuilt). Thanks for any info!

It's possible to do without discharging the system, but ac clutch costs about the same amount as the compressor does(rockauto.com). With that many miles on it, i would just get it replaced for peace of mind. I work on my own cars to save money and a new compressor on rockauto is only $200 brand new. Maybe you can buy your own parts for them to put on to save some cash. Hope this helps.