I have an old series 1 J head bridgeport mill in the shop. We use it all the time. Well today, we went from high gear to slow gear or back gear, and the damn thing makes this horrible grinding noise.
I have looked at everything, can't figure out what the hell has happened. Sounds like gears aren't matching up right in the head somewhere. You put it in high gear and the machine runs like new. You go to put it in the back gear or slow gear and the mill is screaming at you.