82 xj550r Starter whine

Here's the story:
My dad is the original owner of an 82 Xj550 seca. Around 10 years ago, one of the carburetors stopped working and he put it in the shed and let it sit there for more than 10years. I cleaned the carbs, rebuilt the brakes, new brake lines and fittings, changed the oil, and new air filter.
So we fired it up to sync the carbs and there is this high pitched whine while it idles, presumably the starter. I bought a new starter solenoid hoping it would be an easy fix, but it made no difference.

Any ideas? Do I have to pull the motor and work on the starter gear?

 

It might be that the planetary gears in the starter need to be cleaned and lubricated, but more likely it's the starter clutch that is not disengaging. That may go away on it's own after going through several heat cycles. IT's also possible that the sond is something else entirely. A video (with good sound quality) will help if you can make one for us.

 

If the starter clutch is bound up and not free wheeling it will turn the starter into a generator. You can easily verify if this is happening by checking the voltage on the output side of the starter solenoid - the large wire that connects to the starter. The voltage should initially be zero, and around 11 volts when cranking. When the bike starts and the starter button is released the voltage should drop back to zero. If you see a voltage here with the bike running (it will go quite high if the bike is revved up a bit), then the starter clutch is not freewheeling and continuously turning the starter.