I am having a similar issue with PE9 (have not upgraded as I had just got 9 when I built this system and now 11 is out).
I capture videos as mpg and then convert to avi with PE before I do my edits. This worked before but now when I try it, I lose the AV sync in the avi. Also see the same if I watch the video in PE.
I have tried many different project settings but all have the same result.
I am starting to consider a different video edit suite if I can't get a result from the forum.
Okay, I figured something out. Apparentally Premiere Elements 11 just really hated my mp4 file. So I stuck it into Windows Live Movie Maker to turn it into a wmv file. Now it's working fine. My audio and video are staying in sync in Premiere now. So maybe try converting your file to another format and hopefully it'll fix it as well.
OK, I am having the EXACT same issue and it is driving me crazy. When I play in Window Media Player everything is fine but as soon as I play in Premiere everything is out of sync. I have a bunch of files ripped in the same format but only one (that I know of) is having this issue and it seemed to have come out of nowhere. These are my master files and I can't edit them due to the syncing issue. Please help.
As Superdude says, it often has to do with the characteristics of the source vvideo itself, how well it matches your project settings and if you computer is able to keep up with the video playback.
In version 11, the project will set up automatically, based on the first clip you add to your timeline. In prior versions, you have to set up your project manually. Also, in versions prior to version 11, there is no real support for non-camcorder sources, like smartphone and iPad/iPod/iPhone footage.