the hum appeared even without belt.
belt, pulley, platter are like new.
at the moment is very silent but still audible.
the strangest is:
1. the motor is off.
2. no belt on the motor pulley.
3. QC is on (green light/33)
4. after about an hour the motor's pulley gets very hot.
I moved from modern house to the old one with very old electrical
installation... maybe it's something wrong. I didn't feel before
some "electricity" on metal parts after touching.
sorry for my english