Deck going bad -- occasional noises over bumps

[BSOD2600]

I've got a Kenwood KDC-X659 eXcelon CD/MP3 receiver, which I've had in my various cars (moved from one to another) for ~4 years. Lately, I've noticed that when listening to a MP3 cd (yes, they are fine, not scratched, audio is fine on the PC), occasionally when going over rough road, there will be "pops". Hard to really describe besides the fact that there are small gaps/interruptions in the audio. Initially I thought it was a loose wire for a speaker, so I changed the balance/fade to each corner, but it was present in them all. Been needing to replace the speakers anyways, since they were OEM, so got some Kicker DS600's installed. Problem still is happening. When traveling down a rough stretch of road and the problem is occurring frequently, if I switch to the radio, I haven't heard it happen yet (although, I dislike listening to the radio for long periods of time so haven't done a good test yet).

Took the deck out and tugged on all of the wire connectors in the audio harness -- all are snug. Anything else wire/connection wise I should check? Does it sound like the deck's CD/MP3 player is dying?

[evolutionmovement]

Sounds like it's dying. I've had several decks go out at about the 4 year mark, though my Kenwood has lasted 8 years. Doesn't matter anymore since I use an ipod.