Audio Drift on Timeline

I'm working on a project that is a long presentation of approximately 1.5 hours.

Shot on a G5 with audio directly to the camera.

When I play the clip in the source monitor all is fine and the audio stays in sync for the entire clip.

However, when I place it on the timeline (made from the clip) the audio drifts over time so that it is several seconds out of sync by the end of the presentation. I am editing in power points to video track 2.

Any ideas?

Using the latest updates from Adobe on a PC running windows 10.