If you are talking about a mini-jack that connects from the iPod headphone jack, then the prob is with the iPod amplifier. Apple has done an absolutely atrocious job of sound quality in the ipods. the new shuffle has newer amp tech in it and sounds better! But all the rest (larger ipods) plainly suck. I single search in google of "iPod" and "distortion" will give you all the info you need on this ridiculous problem.