If your MP3s were encoded using a different ripper/encoder than iTunes, there may be embedded icon data stored inside the MP3 file. This can cause iPod to read beyond the actual end of the music data, where it will read a portion of another song. Read AppleCare Knowledge Base document #61638 for more information and suggested solutions.
When listening to my iPod, at the end of some tracks, I am hearing random bits of other tracks! The tracks these “blips” come from are not necessarily the following track in the playlist or album, they seem to be completely random. What is going on?