It's possible.
As the belt turns faster, and gets hotter, the "glaze" would no longer hold the belt, so it (the belt) would squeal.
I had that happen on my '70 Trans Am a few times.
Looking the the inside of the pully, where the belt sits, sometimes looks like a clear coat, that's the "glaze".
Not saying it is the reason, but that it could be.
:beach: