Audio on some songs not playing - iTunes Library hosted External Hard Drive

Since moving my music to an external hard drive connected to my Airport Extreme, audio on some tracks will not play. Seemingly at random, songs will just silently move through the track time. Visually it looks as if the tracks are playing, the iTunes timer-cursor moves through the track as if audio is playing. Instead of playing the audio I hear x:xx minutes of silence. If I rewind the song to the begining audio will play as it should. I wasn't having this issue when music was hosted locally. There's doesn't seem to be any rhyme or reason which tracks are play and which don't.

Any assistance would be appreciated.

Cheers!

Lion

Airport Extreme N

iTunes 10.5.1

MBP late 2010