It could be an indication or a damaged or dying hard drive. I would recommend doing a disk diagnostic on the iPod's HD using the instructions given by turingtest2 in this older thread. He also covers what the resulting numbers indicate.
https://discussions.apple.com/thread/3784647?start=0&tstart=0
If necessary, post the results from the HD test and we'll figure out where to go from there.
B-rock