Hey guys,
Real stupid question but can't seem to get solid answer. Basically I am having problems with my radio/cd player (stock single cd player) losing power intermittently / flickering. It happens in 2 situations:

a) Engine is off but cd is playing, as in when i go gas up if i have a cd playing especially at medium-high volume, the equipment will start flickering (radio screen light flickers and music stops/starts intermittently)

b) Engine is ON but i am not moving, eg. stopped at a light. This is especially true if i have headlights and a/c going as well...sometimes if i dont have the headlights and a/c going then it wont do it..unless i crank it real high volume then it might also do it.

Everything goes back to normal as soon as the car starts moving again, and it is only the radio light and the music itself that flickers, all other inside lights stay on.

I'm trying to see what powers the radio if the engine is off? on? on but not moving?
I thought the battery only worked to crank the car and to power things if the car engine is off..so if it only did it then I'd be sure its the battery....but the curve ball is that it does it also when the engine is on but car is stopped.....so then i think maybe alternator? or is the alternator only working when the car is moving?

Or maybe the cd player is going...being in service since 1997 every day...it's lasted a while!

My battery is about 2 yrs old, alternator has never been replaced, radio is stock unit...so I am thinking either of the 3 could be it just trying to see which is most likely the culprit so i wont buy a something i don't need.
Thanx!