Thanks for your response..Were these tracks that you ripped/encoded yourself or are they from a different source? What software did you use if you encoded/ripped them yourself? What format (mp3, AAC, ALAC, PCM WAV, AIFF), encoder (iTunes/QuickTime, Nero, Lame, etc.), and setting (128kbps VBR, -V 2, etc.) were used?
Have you tried converting these tracks in iTunes to another mp3/AAC file and seeing if that has the same issue on your iPod? Just know that iTunes' ability to playback media is not directly indicative of iPod compatibility. For example, I have a 720p mpeg-4 AVC video in iTunes (I actually have several) that playback just fine on my Mac. I cannot sync those over to my iPod. I also have some high resolution PCM WAV files (24-bit 48KHz and a few 32-bit 96KHz) that playback fine in iTunes yet won't sync to my iPod classic (though the 24-bit tracks will sync to my iPad 2).