DGX 500 - scratchy sound in right channel

My Yamaha DGX 500 has cracklings sound in the right speaker. Also in the right earbud. So it’s not the speaker but a board providing either that amplified output or the preamp signal. I have no schematic and am seeking advice on:

Could it be a connection pin somewhere?
If a board is bad, which board is likely the suspect?

Thanks much.

Try cleaning the volume pot

Oh jeez, that’s so obvious and I hadn’t considered it. If it was a stereo amp, I’d have started there. Since it was a keyboard, I froze up! Thanks much!

Okay, I replaced the volume pot, after killing it with contact cleaner (lesson learned there). The keyboard sounded wonderful…for a while… and the scratchiest returned.

I’m starting to search for the other reasons that would cause this noise. Inter board connections, bad capacitors(?), some warmed up component problem? Any ideas much appreciated.

As an added data point this noise has existed for years. It’s been at the same amplitude, not getting worse, but not going totally away either.