Audio delayed on video playback on portable hdd

Hi, I have a 320GB portable hard drive that I formatted to FAT32 (so it would work with xbox 360), recently i've been noticing that almost all of my videos (.avi) the audio in these videos are delayed by about 3-4 seconds. I am viewing these videos on my xbox 360, when I hook my hdd up to my computer and run the same videos using VLC media player, the audio is NOT delayed. The videos used to work fine on the xbox 360 and the audio was never off, but now it seems like all of them are delayed and watching anything is difficult as you'd expect. Is this a known problem, does anyone have any advice?

Thanks!