I seemed to have had the same problem. My iPod Nano (7th Edition) would start pausing itself after a couple of seconds of playing music. I would unpause it, it would play a few more seconds, then pause itself again. Sometimes, the music would even start to skip like a scratched cd. It only happened when I had it connected to my car or other auxillary speakers. It never happened with headphones. This baffled the **** out of me because the iPod was brand new.
Anywho, I had heard of TVs (I forgot which ones) that turn themselves off when too loud. I didn't understand how lowering the volume would help, but it seemed similar enough to my situation so I tried it. And sure enough, it fu**ing worked!!! It makes sense because I never had the volume at 100% when using headphones, but i did when using my car speakers or other speakers. So now I keep the iPod's volume level at like 80% (or lower) and it doesn't happen anymore.
I can only imagine there is something within the software, sensing the volume of the files themselves, and pausing the track when it hits a maximum level. Maybe it's a safety feature.
--IVAN