Right tweeter speaker static on about a dozen consecutive keys in mid-high range

by info@siamlotus.com
(Atlanta, GA, USA)

In my circa 1990 Yamaha Clavinova model CVP-30, lightly used and not played for years, I am now getting right speaker static on about a dozen consecutive keys in the mid-to-high range (high C and up) when either volume is turned louder than middle setting, and even when volume is turned way down and the keys struck hard.

When the piano top cover is unscrewed and folded back along its hinges, a stethoscope at each speaker can pick up mild static from all speakers, even when no keys are hit. But this sound was not detectable when the cover was closed.

This became apparent when I was checking out the CVP-30 (international model with 4 voltage settings possible -- 110, 130, 220, 240) in order to sell it.

The problem remains at the right-side tweeter even when switching tweeters right-to-left, and when switching speaker cables right-to-left at the amplifier.

No record of any spills of liquid among these dozen or so keys. Keyboard actions all seems fine.

Any ideas where the problem lies? Keyboard? Amplifier? Main mother board?

I would prefer to sell it in perfect playing condition if the repair is not too difficult or expensive to do myself, such as replacing a component. Otherwise I would sell it as is and let another fix it or cannibalize it for parts, as it is otherwise in excellent condition, with very little keyboard use over its lifetime.

Bruce