This just happened to me this past spring. Same popping sound, then the sound would come on. After a while the popping and cracking would not play at all, and eventually the music stopped.
"I can't remember if I cried...but something touched me deep inside, the day the music died" - McLean, American Pie
Worst yet, I took it to the dealer, they spent 1.5h, only charged me for 0.5h (GoAuto's Ericksen Nissan, Edmonton) and the burnt out the 20A fuse under the hood. That keeps the system coming on, but there's still something wrong with the amp.
Did you get anywhere with this yet?
'04 Max (6 speed)