Hi! I added Nike+ this morning and now my Nano won't play the music normally. It sounds like background music, I can't hear the words to the songs. I don't know if putting in the Nike+ has anything to do with it. Thanks for the help!
Check the iPods setting for equalizer (turn the Eq to OFF) and also check if there are other setting on the iPod like Sound Enhancer you find you iTunes (my iPod is older than yours so I am not sure if they added Sound Enhancer to newer ipod or not).
try going to settings. playback. make sure sound check is on. make sure eq is off. if these things don't work, i suggest you bring it in. also, look around on your computer, it might have caused it. hope this helps.