I've never used Quest, but from what jaynabonne said here:
You can have the sound continue on into the next page. if it's not
looping, then it will stop eventually.
I'm wondering if you could take another approach, rather than looping the sound.
If Quest doesn't do fades, what about creating a sound file that repeats the sound a few times, and then fades out? With a free sound editor like Acoustica Basic http://download.cnet.com/Acoustica-Basic-Edition/3000-2170_4-75741708.html you can put in a fade yourself. Then in the story, just play the sound file once, and do what jaynabonne said as far as continuing the sound to the next page.