2006, LT with 55K miles. The problem is not always present but does occur very frequently.
When accelerating, my A/C compressor whines loudly and can be heard in the cabin. When it's in the "whine mode" the engine idle is rough like when waiting for a red light to change I often shift to neutral to smooth out the engine. Also it feels like I have to ad more accelerator to maintain 60 or 70 MPH. The noise is very noticeable when accelerating but not so much after reaching highway cruising speeds.
I'm quite certain it's the compressor because the noise is completely gone when the A/C is switched off and the overall performance is noticeably improved.
The cold air output is perfect and has been checked with a thermometer, it's the whine that bothers me and I am concerned that the compressor could freeze up and bust my serpentine belt.
Anyone else have a similar problem? I hate to take it to my rip-off local Chevy dealer who gets an hourly rate of $94. Any info will be very much appreciated. Thanks, John

 

Here are a couple of threads on A/C compressor whining, they can be a bit "vocal" on the Ecotec engines, but you might have something going on. There was a TSB issued by GM on compressor noise so you might want to check with the dealer as it may be still covered by GM. The rough idle and additional drag you're feeling have me thinking that there might be an issue with the compressor clutch also, its supposed to cycle and it might be seizing up on you.

https://www.chevyhhr.net/forums/problems-service-repairs-42/whining-noise-when-c-compressor-25140/

https://www.chevyhhr.net/forums/problems-service-repairs-42/whrrrrrring-noise-when-c-compressor-running-9734/