iPod problems (mp3 players)

*I've owned my iPod Classic for a couple of years now with very few problems and have enjoyed it immensely. The only problem that seems to continually happen is when I hook my iPod to an mp3 player such as a job site radio. What happens is that a song will begin to play and out of the blue at some point in the song, it'll skip to the next song before the one that was playing had finished. Conservatively I'd say it happens on 3 out 5 songs. It may happen 20 seconds into a song or it might play almost to the end and do it, but ultimately it will happen. Now, I don't know if this has anything to do with it, but the way the iPod hooks to the job site radio is through the headphone plug in. The reason I bring this up is due to the fact I have several devices I hook my iPod to but they hook to the other end and I never have problems with it. It's also not the job site radio either because a friend of mine hooked his iPod to my job site radio and it never skipped. Suggestions, solutions anyone?*