How to correct audio buzz from casette player?

Old Sharp SG-3 casette recorder/radio/record player that I'm trying to repair for my father in law. Just put on new belts but when the tape select button is depressed with or without the casette running, there is only a buzz from both the L & R channels. There is no music being heard when the unit is playing either. Just buzzing. I sprayed tuner cleaner on the pushbuttons that seemed to help ever so slightly, touched the head with a screwdriver and it created a different and additional buzz. FM, AM and record player sound fine. No visible damage to any part or to the board itself. Any suggestions? Thanks