One of my players here was noisy last winter.

Until I took it apart and found the connector pin that was just hanging by its last thread of wire, and recrimped it.

Check and double-check the internal wiring harnesses, that go between the mainboard and the docking connector.

If you're using the RCA outputs, then check for loose solder joints between them and the mainboard -- I had another unit with that problem once.

Cheers