As others have pointed out, it could be due to the metadata embedded with the MP3. Sometimes, tags other than ID3 are attached to MP3 files. I’ve heard of APE tags and Quicktime tags causing problems like this. When a player doesn’t know how to interpret them (in this case, the Fuze), it usually treats it as audio data, resulting in a momentary glitch or pop, typically near the beginning or end of the song (depending on where the tags are stored in the file.)
Players that recognize this data as tags (WMP) will just pass over this data.
I’d try removing any unneeded tags / metadata from the affected files. I’ve never had to use it myself, but I’ve heard MP3tag does a good job with this.
