At the risk of being flippant, I think the help you need might be from a pest exterminator.
There is only one part inside a CR-420 that's capable of anything like self-locomotion: the protection relay. That should only make a quiet click a few seconds after you turn the receiver on, and when you turn it off.
If you're hearing something loud, my suggestion is to take the receiver outside, put on some thick gloves, unscrew the wood cover, remove the cover, and see what comes out. Really.
(Is that a head-scratching emoticon? That's what I intended.)
Cheers,
chazix