RE above

AMMETERS are NOT grounded. You probably washed the lube out of the bearings, or maybe there's a damping hairspring, I don't remember, that broke, etc.

Probably nothing to worry about. One thing you could check is reach up there and disconnect one wire, then temorarily wire in another meter to see if they both act up, or you MAY be able to tell by simultaneously watching a voltmeter. If the voltmeter surges up a little in time with the ammeter, then you have a regulation problem. If the voltage is pretty "even" (slow to change) while the ammeter is "fast" then you have a damping problem right in the meter