Thank you both for your replies, and thankfully after a little messing about I've fixed the looping problem.
If you import either ogg or wav in as music, then trigger this as looping, there is a slight delay between each loop.
If you import either ogg or wav in as a sound, and trigger as looping, it works absolutely perfectly.
I've uploaded a quick video to YouTube of both imports. This probably wasn't the ideal loop to use, but it does demonstrate it working one way and not the other