@petert913, I've had no end of problems with my zeq25 as well.
Are you balancing your OTA precisely? If it's not well balanced then you might be overloading the stepper motors, in which case the motors would skip steps without sounding overstressed. I don't know if or how the cem25 detects and reacts to the motors skipping; the mount might not report it at all. If your belts were slipping then you would definitely notice the extra noise.
It could also be a low voltage problem. Try to find a bigger (higher amp rating) 12V supply or battery.
Edit: watched the videos; you're right, seems to be a function of output position, but the worm gear teeth look clean, so either imbalanced or a problem with the worm itself. Maybe try realigning the worm: https://www.youtube....nuGQNYS8&t=709s
Edited by rkinnett, 25 January 2019 - 09:00 PM.