2002 Pathy Rear Speakers Crackle & Pop when Engine is Off

[02SurfPathy]

Help! My wife told me one night that there was something in the car under the back seat making a lot of noise. I will not go into what I was ready to do next but it turned out to be the rear speakers. This does not happen all of the time. My battery has been dying so I was hoping these were related. Now I only think the relationship was that somehow the radio/amp is draining my battery. I just had the battery replaced and still when I start the car, the stereo comes on and the rear speakers pop/crackle then everything sounds fine.

I have even tried to turn off the stereo prior to turning of the car and this problem still intermittently happens. It did come with the Bose stereo with the CD that had developed the CD problem. The stereo was replaced years ago and this problem with the popping is pretty new. My wiring of the replacement stereo connections are soldered and heat shrunk.

Any suggestions of where to start looking. How is this happening if the power is off to the stereo?

Thanks to all for any suggestions!!