Kenwood KR-5600 receiver, just finished recapping Audio and Power Supply boards. After resetting bias it started making buzz/hum in a rhythmic pulse that would vary speed as either the Volume or Bass control was moved. Right channel only. Maybe some transistor oscillation? Haven't had one vary speed like this before. Any ideas where to look or what to check? Voltages I have checked so far have all looked pretty good. KR-5600 has op-amps for preamp section, and audio controls on the PCB with power amp. Tuner seems to work fine, unaffected by the problem. Any help would sure be appreciated! It's a good puzzle.