Here's a question for you:

Does the thump happen the instant it snicks into the cradle, or does the thump happen as the player boots and comes out of standby?

If the former, then it's definitely a mis-wired installation where the remote amp wire isn't doing the job it's supposed to do. If the latter, then it might be a faulty amplifier or something wrong wth the 'peg itself.
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Tony Fabris