Im not fully familiar with the inside of the GTO doors but I have worked on quite a few other GMs Buicks etc....If the GTO has cable operated window regulators this sounds like your problem. From the crunching noise your describing it sounds a lot like those other GMs. They have a power window motor which runs a set of cables, almost like bicycle brake cables, and they tend to bind up and come out of place inside the door. Chances are you will need a new window regulator.
06 GTO IBM 408 Stroker-Sold
06 Corvette, Supercharged 607whp, RPM trans and Diff, RPS twin disc, Z06 susp, Dewitts Rad, Custom Fuel system