I don't have anything to add except that I have the exact same problem
on my 2001 Wagon. It is very intermittent. The radio seems to lose
power completely and then come back on a few seconds later. Once this
starts, it happens repeatedly and then usually it shuts down altogether
for a while.
I have sort of noticed that it coincides with hard braking - which
lends credence to the loose connection theory. If I get around to
tracking it down, I will surely post my findings but I may have to wait
until the problem gets worse.
I also have the well-known speed sensor problem. With the AVC enabled,
the radio volume surges and fades with the wildly swinging speedometer.
I doubt the two problems are related but in combination, they make the
sound system seem a little posessed.