Raiden II Squealing Noise

Recently my Raiden II has been making a squealing sound after it has been on for a while. However, it has happened immediatly upon powering up. No other board in this cabinet causes this sound. It's not a steady squeal or high pitched sound. It sort of...changes dynamically and it is coming from the mono speaker itself. Also, the games sound still comes through at a rougly equivalent volume.

Any help would be greatly appreciated.

Thanks in advance!

I have the same board with the same fault, ended up replacing the audio output IC and all the electro caps around the audio stage and it did not fix it, even though freezing the output IC seemed to clear the fault.

Out of frustration fitted a larger heatsink which seems to have "masked" the problem, if you do identify the actual faulty component please let me know.

Sounds like a corroded ground somewhere.