Please have a look at this LoopMash video tutorial:http://www.youtube.com/watch?v=5U3i_7I5YOA
I hope it helps.
Once I didn't hear anything as well and then I realized I had the mute switch activated on my iPhone.
After I deactivated the mute switch I could finally hear LoopMash.
By the way, have you checked the help page inside the app that pops-up when clicking on the "i" on the upper left corner of the matrix page?