I came across a servo that looks like that one recently doing the same thing. We ordered in a new motor to replace it but before doing that we took the motor off to see if we could find anything. I think there must be a magnet thing inside because when we gave it a shake to start with there was a rattle noise but then it stopped rattling. We thought well lets give it another try on the machine and it then went fine. Its been going strong now for maybe 3 months without any noise. Maybe the sudden stop they do sometimes shook the magnet loose, I don't know. He now has a backup motor if needed now but means he would have to drill some new table mounting holes etc which is why we tried the other old one first.