Alright. I got a 97 Dodge Stratus. 4 cyl 2.4L. 101k on the odometer. The squealing on idle, which I think may be a pulley or a belt, goes away when the tank is above half. Wife literally just reported it made a slight noise(squeal) on idle on her way to get lunch on her lunch break. Tank was just above half. When we filled it up - the noise went away.

Wtf?? Help!

 

Id start by inspecting the belts and pulleys.

 

THat's what I was thinking too. The serpentine belt is fine - It looks brand new. I know it's one of the pulleys, but WHY would the noise DISAPPEAR COMPLETELY with a FULL TANK OF GAS? Makes no sense!