Billy. I need help. Sewing a back pack with my Singer 191 commercial machine. I guess I left it on too long and the motor overheated. It started to squeal and make all kinds of noise. Turned it off and let it cool down over night. Turned it on this morning --no noise. Sewed one inch (sews fine) and it started squealing again. No over heating now just squealing. Turned it off. Any idea? I sure don't want to burn it up.