Most have been mentioned but as i had grinding issues with my HEQ5 i thought id list all the possibilities:
- Power levels too low. Check input voltage.
- Worm gear too tight. Shouldn't be a problem unless you tuned up the mount.
- Clutch overtight. You shouldn't need a hammer to undo the clutch...
- Too much weight. My HEQ5 couldnt handle an ED127 + CCD + guide scope and would grind gears. Make sure your not overloading the mount.
Once i identified my problem (worm gear too tight + over weight) and rectified it, the mount runs perfectly.