The sound as far as I know that you are talking about is the Tinnitus and it is the constant ringing in your ears that is always there just is masked my almost any sound at all.
The purpose of listening to it is to keep your mind off your body but I too find that my mind wanders when I listen to it for extended periods of time.
What I like to do when I perform WILD is to let my mind wander while telling myself every once in a while that I am not awake, sometimes I will get where my breathing starts to get under control of my SC but end up noticing it and have to start over.
Another thing you can do is to count or repeat some phrase, it can be as long as you want as long as you can remember it and
it involves dreaming in some way.
You should make up your own styles too, but if nothing seems to work for you perhaps WILD is not the technique for you.
EDIT: You can also look at the WILD topic Here for more information.[/url]