I have had this problem for almost 3 months now. And guess when it happened to me, a month just before my warranty ran out. Creative were trying to hold me from sending to for repairs under my warranty, by telling me it might be the headphones itself. Tried another pair, still muffled sound. So warranty has just run out. So i asked Creative to give me an address where i can send my Zen for repairs in England. No reply for a week.