audio starts changing towards the end of projects?

Hey guys. So Ive noticed something that seems to keep happening in all my projects. I'll go through and sync the moventments and lipsyching with the audio and it matches up perfectly, then whenever i render the videos the sounds and movements suddenly changing. Like the lipsync that i had perfectly lined up is now a second behind or ahead even though i havent changed the timeline. The only fix i can find for this is to switch the audio to "raw" but that makes it sound crappy. Ive also started noticing it happening while i'm working on a project. Like I'll have a layer lined up perfectly with the audio, so i lock it. Then the next day it starts getting off towards the end of the video even though both the layer with the movements and the audio layer are both locked. Anyone else having this problem?