Given that it's working, I'd be inclined to let it go until it craps itself, clean out the condenser, and install another (or do a Sanden upgrade) when the time comes. Reciprocating compressors moan and growl. It's just part of life. The one on my SDL moans at exactly 1500 RPM on the tach (which happens to be driving 30mph). 50RPM on either side and it's silent. My '96 Exploder had a very loud "rattle" from the compressor when it ran. Went over 40K miles from the time it started making the noise until I got rid of the car, never a problem other than the noise under the hood.