LOUD HUM IN AUTO-REVERSE BAY

My bedside Sony has developed a loud hum on the 'play' mode on the auto-reverse bay, which I use a lot. What to do? I can't even hear some of my environmental tapes because of it. Might this be a problem in the power source? The other bay plays just fine, though. My health is progressively getting worse, and that old boombox comprises a lot of entertainment for me. Any advice will be gratefully received...

That bay may have a broken ground wire for the head or deck.