The Origonal Head Hunter wrote:don't use mp3s for editting, conver it to .wav format.
While some versions of WMM don't like MP3 the problem is actually more likely due to whatever compression is on the audio- WMM doesn't compensate for bad audio.
Converting the audio to .wav will make it bigger, but might not help if you've got a bad source.
Also, if you're talking about playing it when the footage is on top of it, you've got a completely different problem- it's called lag and WMM is like that. to check if you're lagging, export your project, if the music is miraculously working again- you're audio's fine, its just the program lags.