iPod makes scratching/static noise

I got my previous iPod replaced because the headphone jack wore out. Upon receiving my replacement i found out that, after spending an hour or two in my pocket or in any slightly warmer place, the music the iPod was playing would become scratchy, static-y and eventually the iPod would go silent. It would still keep playing, but it would either not make any sound or make horrible static screeching noises. It isn't a jack problem because I just got new headphones, and the sound goes back to normal if i keep the iPod somewhere colder for a little while. wondering if anyone knows how to fix this, or if i should get this fixed. and if perhaps i can get it fixed without paying shipping, since i received a product that was faulty out of the box.