RAM Preview Suddenly Plays Out of Sync

A little history on what happened - I started a project in After Effects CS6, and have worked on it in exactly two sessions.  During the first session, I added two clips of footage, synced them to a track of music using RAM preview, compiled a test render with satisfactory results, and then quit the application.  Upon opening After Effects again during the second session, I found that the footage and audio no longer appeared to be synced in the RAM preview - the footage seemed to be lagging behind the audio.  I again rendered out a test of my project, and in the resulting file, the elements were still properly synced with one another.  I've tried to figure out what is causing RAM preview to play out of sync to no avail.  So far I've only deduced the following:

• The composition settings and the RAM preview playback settings are both at 24 fps.
• Ram preview plays out of sync in exactly the same way each time, (the offset between the footage and the audio remains the same length, and there is no unpredictable choppiness or lagging).
• The audio plays at the proper tempo, leading me to believe that the footage is somehow slowing and causing the issue.

Many of the similar-sounding problems I've found on this forum suggest that After Effects is running out of RAM, but my project is far too small for that to be the issue.  On top of that, I haven't changed anything since my initial session with the file, when it played perfectly.  That's about all of the pertinent information I can think of relating to my problem, but if anything else might shed more light on this, please let me know.

- Dominic

After Effects CS6 (11.0.0.378)

Windows 7

Intel Core i7-6700K CPU @ 4GHz

16 GB RAM