I just checked all the audio enhancements, and they were all off by default, so just to be sure I turned them on and then off again to see if that made any difference. Unfortunately, it’s still having the same problems as before.
As for the stutter, the videos did play normally inside Vegas, although I also discovered that VLC has different problems to Windows Media Player, as it turns the image grey and pixellates it as opposed to just the stutter, so I’m glad to know at least the video isn’t corrupted in that way (probably). However, I would like to be able to view the video normally, so if anybody knows of any media players that can handle Sony Vegas’ AVCHD/.m2ts files, please let me know.
Thanks a lot for your help, Danny.