[QUOTE=JAZZCNC;115603]It would be a mistake not to check it out.

BINGO and thanks to JAZZCNC. Disconnected the drives nuts and jogged for about 10 minutes with no knocking noises, gave them a liberal spray of silicone lubricant, reassembled and all seems sweet.

So, is it possible to replace the stepper motor with one with a bit more gut? I can't see any markings on the current ones.