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I don't know, sorry.
I'd bet money the problem is capacitors. Either SMT electrolytics on the motherboard are bad, causing any number of malfunctions, and unless they've been replaced, they *are* bad. Or the output filter capacitors in the PSU are bad, causing switching noise to make it out of the power supply and eventually work its way to the speaker. Every LC series of this vintage that I've been inside recently has had bad capacitors. Replace *all* of the SMT 'lytics on the MB, and all of the output filter caps in the PSU. The PSU caps are clustered together on one end, most of them are probably leaking brown liquid by now. It's less than 15 bucks in parts to replace all of them and the SMT ones on the MB and it's the only way the machine will ever be reliable.