High pitch whining sound under hood in hot weather

[m4dc0w]

High pitch whining sound under hood in hot weather.

I'm guessing that it is my AC compressor bearing, but haven't had a chance to check it under the hood, and when I do the sound isn't there.

Any suggestions?

 

[Black92LX]

try a new serpentine belt. i had the same problem threw on a new belt and it went away.