Hi, first time poster.

I'm writing on behalf of my Grandfather, who's KN-5000 has started to produced a horrible electronic noise from the left speaker. Sometimes when the keyboard is restarted the sound will work fine again, then after a number of seconds crackles and pops can be heard before getting quickly worse. I've opened the top up and given all the components a good clean, as well as plugging into another socket, but to no luck. Moving the volume slider bar at all seems to escalate the problem too.

Any insights would be greatly appreciated!