I just noticed this today; yesterday I went for a 3-4 hour ride and didn't hear it, but I had my headphones on.

Its roughly 50 degrees. I get a small, slight chirp on the left side immediately after letting off the gas. It almost sounds like a squeak from *something* after being under tension and then not.

88ci, 5 speed.

 

Your belt is too loose.

 

yes Check the belt