Any of these can cause sync problems:
capturing to USB hard dives or slow external/internal drives
Running other active applications during capture (word processors, etc.)
Processing/playing another video during capture
Capturing to the operating system's hard drive
Too many PC attachments drawing power from main PC
Hard ddrive defects
Heavy CPU usage problems or overheated CPU
Enabling
VirtualDub a/v sync timing management (
http://www.digitalfaq.com/forum/vide...html#post45242)
Starting VDub capture with the "F5" key (compatibility audio mode)
There are other causes. How can one list them all? To say that "nothing was changed" is likely not accurate. Something always changes or gets changed.
Always quickly review captures for things like correct sync at begin, middle, and end,
at the time of the capture, not 6 months later.
Video and/or audio editors can change audio timing, so I hear. I never had the problem, so can't help with audio edits.