Hi, thanks for the reply. My sample has bevelled edges at the moment, but when I select it and then press CTRL+L, nothing happens. I tried right-clicking on it and selecting "Groove-Clip Looping" from the menu instead, which would normally switch it off, but this has no effect either.
Edit: I've discovered that this problem applies to some .wav files, but not others. It seems to depend on which sample pack they came from. Perhaps in some sample packs, the files all come with looping information embedded in them, which prevents Groove-Clip Looping from being switched off. This would explain why I've been having this issue only recently, because I downloaded a new sample pack and have been trying to use those files. The files from my other, older sample pack still work fine.