My car has topped 100k miles and I had noticed this squeaky, slipping belt like noise for the last few weeks. somehow, it seems to have gone away. Wondering if this is a good thing, or bad.

Recent changes -

Topped off Coolant - added about a cup. There seems to be a small leak from the sensor near the radiator
Topped off CHF - reservoir looked almost empty.
removed my license plate holder and put the tow hook cover back on, hoping it would improve my aero and return slightly better mileage.

Fire away with your speculations please.