TerminatorX5 gave you a good tip, suggesting you to examine the radio module connector.

On my X, I had that problem of speakers fading, and coming back to life, sometimes there was some crackling in the speaker.
When I removed the radio module plug, I looked inside the female pins, and found light oxydation on them. I sprayed some contact cleaner (shake to remove the excess) re-inserted it / remove / re-insert /remove, re-spray contact cleaner and redo that a couple of times, and no more problems.

You may have to remove the CD changer and the NAV to access it though.

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