2002 Chevy Suburban Abrupt power out

Usually in my burb when I park and turn the ignition off, the radio will still play until I open the door.
For the past two days, when I would turn off the engine, there would be a pop sound like pulling the plug on a stereo, that I hear in the speakers and everything goes dard - no radio, clock and the usual info center orange LED paned would say security - but now completely black. I put the key back in and it starts just fine.
Went to Autozone and there are no bad diodes in the alternator and the battery (1 year old) is still strong.
I appreciate insights into sorting this out.
THanks