Does the sound come from your speakers, or the CD player itself?

If it's coming from the CD player, it must have a relay muting the output, and the sound is just the mechanical sound of the relay operating, which is normal. If it's coming out of the speakers, either the muting transistors have been removed, as Mr F. has said; a mod often done for better sound quality, or the muting isn't working. If it's this, I don't really think it would be worth the cost of having it looked at.

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