That is an extremely common problem with the in-dash 6 cd for the 02-03s. Its a wiring issue with the pre-amp for the cd player within the head unit. Nissan and Clarion have not really addressed this issue except to replace the HU under warranty, but in most cases it comes back again. Here is some info on the fix:
http://forums.maxima.org/showthread....hreadid=189182
But it seems that the cheapest/easiest fix for many has been to go aftermarket.
I've had 2 HUs replaced under warranty and my 3rd one is beginning to crap out in exactly the same way both of yours are, so one day I may decide to give it a shot.
Here is a link to the TSB for the 02-03s:
http://maxima.theowensfamily.com/tsb/NTB03-017.pdf
I've never heard of this issue for the 01s, but it sounds like its the same thing that's happening to us 02-03s.