Its not silent but not noisy either, about like a fridge. The motor itself is about the size of a matchbox within the housing

Something like this but bear in mind 3rpm is too slow to use and needs gearing up to 12-25rpm.

DL-MOTOR30 Mains Powered Mirror Ball Motor 3 RPM SPEED on eBay (end time 25-Mar-11 08:03:31 GMT)