I have a 60 and a 20 gig unit and, I can recreate this problem on both units every time.

If i'm playing a wav file and pull the unit from the sled and then re-insert it, when the wav file resumes play, it plays for approx.30 sec. and then pauses play for approx 5 sec. and then resumes play.
Also, if i'm playing a mp3 file and them select a wav file , it will do the same thing every time, play the wav file for approx.30 sec. and then pauses play for approx 5 sec. and then resumes play.
I have had this problem with wav files with all versions of the software and have tried this with and without hijack installed.

So, is this a possible hardware problem?