Sony Betamax audio problem

[Chad Hauris]

I have noticed a problem on several of my Sony Beta VCR's. Most of these are the BetaScan top loading units with mechanical controls, a row of varactor channel buttons on top and the "fast play" feature (can't remember the model number) but it has happened on a later front loader too.
Audio is either weak or mixed with fuzzy noise. Occasionally one of the machines will have a whining whistling sound in the audio which goes away if it's tapped.

Could this be a bad cap or other electronic problem? Cleaning does not seem to help. Video is good...just the audio is poor.