Rear speaker problems - 90q20v

[Solomon Ngan <sngan@netaccess.on.ca>]

Hi,
I have successfully upgraded my front speakers.  But I still have a
problem with my rear speakers.
The problem is intermittent "cut-out" from either the left or the right
rear speakers.  I usually correct the problem by cranking the volume up
and down several times.  But this is only a temperary fix.  The problem
come back after a while.
Again, this problem is intermittent.  Either left or right ???
At first, I thought it's the amplier (rear speakers have integrated
amps).  However, it would be extremely odd to have both speakers acting
the same way.
Could it be cold solder, or dirt in the deck ??
The deck was looked at by a car stereo store, they did not spot anything
for now.
Any suggestion ?
If I were to replace the deck, can I keep the rear speakers (and the
ampliers) ?
Anyone has similar experience ??
Thanks,
Solomon