Other apps running: Facebook, gmail, bbm, and the built in email and calendaring.
Here's what I do and it seems to always recreate the issue. Fire up the app, change to crickets, set the timer (1 hour), turn the volume all the way up, plug the phone in (brings up the clock).
After 5 minutes the sound goes silent for a few seconds then comes back. Then again exactly 10 minutes after starting the sound completely stops. The only way to get it back is to interact with the phone.
The purpose of buying this app is to have the sound in the background and not have to think about it. If I have to interact with the phone every 5 minutes then it won't help me sleep any better.