i recorded 40 min interviews on a ex3 and the audio separately on a H4 zoom. Once i've synced the audio in FCP its fine but slowly starts to drift . at first i thought it was the sample rate because the audio was recored at 44.1KHZ and the video audio is 48.KHz but when i up sampled the external audio to 48.KHz the audio still drifted, so I thought it might be because the audio was in WAV format so i converted it to Aiff, this fixed the drift a little but it was still there. I have no idea why this is happening? Can anyone help me out, thank you in advance.