Sony KV32S66 Sync hum on all inputs left channel line out low.

I have a Sony KV32S66 with an audio problem. It has a hum (not 60hz,but like a sync hum) coming from the built in speakers which doesn't change with picture changes. It does go away if the unit is muted or the volume is turned down all the way. It doesn't come out the line outs on the back, but the left channel is very low. I've asked on other message boards, but no one has dared to try to help. I've worked on professional broadcast monitors but not consumer tv's with audio circuits. Any help will be greatly appreciated.

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