Oh man I was a victim of that too, but I'm gonna tell my end of that story anyway. I have a Duo-R now, but I used to have a Japanese black Duo.
If it wasn't the AV jacks there is that manufacturing flaw that NEC did that's the cause of this problem. On black Duo systems, the A/V plug is located right next to the power supply. Not good. After several hours of play, the A/V jack catches heat and that's what causes the static crackling and eventually....POOF! No sound.
I know it may be too late to say this, but that's why the Japanese white Duo-R/RX is the best (which can't play USA cards w/o a mod or converter), the A/V jack and power supply were relocated far away from each other.