We can't get the voice audio to synch with the video when rendering.

We are using VP9.0b. We are rendering out to an MP4 (original video 720x480x32) using the MainConcept AVC/AAC (*.mp4) output setting.

The audio appears to be perfectly synched in veg format - checked using Dynamic RAM preview.

Is this a memory setting on my computer? Output setting? Any ideas?