nothing in the electrical diagnostic manual about this.
I get popping in the speakers even when radio is not on
(If I turn the ignition switch to ignition then back to off I
get the popping sound). I have switched the speakers and
still get the popping when I cycle the ignition switch.

 

I get it too.

 

Took the speakers out and tested with another stereo. No problems.
Called the radio manufacturer, and found out that the amplifier is
suspect. The amp has power even when the radio is not on. I sent
the radio in for repair.