Hello,
We have had this problem in the past with this model, (sounds like inverter buzz on sound, and muting the sound will remove/lower it), it is very intermittent, and can go for days with no problem.
We have had some success by changing the caps. on the Audio PCB, the Audio PCB itself (18AMP06-4), or the Power-Supply (17PW20v2). These boards might be the starting points to check.
Regards,
John