2002 Sable underhood whine

At 60K miles, I have a whine that changes pitch with engine speed as you accelerate/decelerate, and only occurs with the air conditioning on. The Dealer has replaced some transmission planetary gears. Didn't work. Then they replaced the air conditioning compressor. No change. I bought a mechanics stethiscope and listened to the alternator, the tensioner and the power steering pump. Couldn't really tell for sure. I was going to just replace the alternator, but thought I'd check the Forum first before spending the $200.