Okay, it's something to do with my air conditioning, but not sure exactly what.

When it's warm/humid out it does this, when it's cool it's fine. But from 2-3K RPM it sounds like the engine is working harder than it should, sounds like it's at a higher RPM, but it isn't the engine. If I flip off the AC it goes away immediately. Any clues to what this is? Compressor or something?

 

i dont think it is but maybe it has to do with your fans?? whenever the a.c. is on it automatically turns on the radiator fans.....

 

Doesn't sound like a fan. I can get the engine warm and then turn off the AC and it does the same. The radiator fan should still be going with the engine temp up over the middle of the guage. If it isn't then there is a problem :P

 

A/C compressor or the clutch bearings might be going. You might just have a bad drive belt too.

 

My car got louder and louder when I was driving and it turned out that the A/C pulley and belt was almost dead. Check your belts. Had my pulley and belt replaced for $90 w/ labor.