I have a potential idea…as I had the exact same problem not to long ago.
Check in your *info* pallette, are you playing at real time? If not, the audio will be out of sync of the video within after effects, but not in your render. You will notice a black “real-time” or a red notification that you aren’t in real time.
Your options to see a RAM preview with audio in real time is to lower the resolution and scale of your preview window until your machine will play the comp at real-time.
This worked for me, and I hope it works for you…I think the idea is that AE will play frame for frame…real time when it can, but when it can’t…it just plays less frames per second, it doesn’t skip any to play at real time.
-Jason
Let me know if I helped.