I have been using a Sony ICF-9740 AM/FM table radio on my nightstand since 1974. Recently, there is increasing interference on the AM band. It’s not AC “buzz” or “hum” that one would expect from old power supply filter caps; it's more of a high frequency whine — my guess is around 6-8kcs, and it's consistent even when the volume is turned all the way down. I could replace this unit but I would really rather fix it. Any pointers on finding the source of the noise or theories on what might be causing it?
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