FRIDAY126

Recently picked up a used (but seems well maintained) Bosch 4hp table saw. Probably about 4 years old. Sturdy contractor grade. Works fine BUT when turning the blade elevation and angle wheel to raise the blade as the wheel turns it tightens until I hear a popping noise then it loosens momentarily and repeats the process until it gets tight enough to pop again. The blade does still raise and lower but figure something in there maybe about to break. While lowering this doesn't happen and it moves smoothly. I've thoroughly hunted around on the under side, cleaning off gears attached to the wheel and shaft behind it and looked for anything obvious/damage. Any thoughts guys: next trouble shooting steps, something obvious I maybe missing, etc?