I have the same issue with my wii. It is NOT the cable, I tried the cable off another wii that worked perfectly fine and I still had no sound on mine. I have also tried different ports and they all work. I still have no answer whats wrong but I can say for sure its NOT the cable.
Could be the bum units they put out from shangai's drugland...
I try to make my posts clear and easy to understand so they don't sound like "imA gonsdds 2yuz shvsdfoool" or whatever 2cuokls4usz crap most ppl speek in the land of brooklyn nowadays.