What causes Audio to go out of Sync?

So this happened to me yesterday when i finished rendering. I thought it was just one problem so i recorded my footage again and bam, as soon as i import it in Premiere, its out of sync in the peview by about a second, same thing if its rendered. the source files all work fine when i play them back on my computer. Seems to work fine in Vegas 9 but that software has given me a ton of problems in the past and Premiere is so much better. Heck i even downgraded my 5.5 for this. I tried uninstalling my 5.5 and reinstalling just 5.0, still got the sync issue. I needed to have this project rendered yesterday so its a big problem. I’m using M2TS files but ive been doing that for the past year without this problem.

My first thought was a codec problem but the main reason why Vegas is so bad because the only thing they change in updates is the gooey and its stuck with really old codecs and that works fine.

via Video Editing Forums: Digital Director – Adobe Premiere, Premiere Elements, and After Effects http://www.videoforums.co.uk/adobe-premiere-premiere-elements-after-effects/42703-what-causes-audio-go-out-sync.html