I have a 2000 C5 w/ about 50k. I read some posts here and elsewhere about a
persistent "squeak, squeak squeak" under the hood. One fellow, Steve, said
it was the crank pulley/harmonic balancer being wobbley. I checked it out,
stopped by the dealer, and wanted to share what I found.

All C5 harmonic balancers are wobbley. It probably isn't that -- which is a
good thing because out of warranty repair is $650.

Check the AC belt -- that's what it was in my case. I'm in the process of
getting a new "gatorback" belt (cross groved). It could also be the main
serpentine belt or even the tensioner. To find the difference, put a socket
on the tensioner belt when the engine is running (tighten) -- be careful --
and see if the extra tension causes the noise to go away. If not, remove
the AC belt (cut it) and start the engine. If the sound is gone, you know
that was the cause. (It is time to replace the belt anyway - my opinion).

Hope that helps the next guy.

Dave