The ads are too obtrusive

Im talking those large ad pages that pop up spontaneously (I forget if the ads have that 5 second countdown, so you have to wait to close the ad. Obnoxious. Of course, there is the 99¢ upgrade offered here, which is a reasonable price...

Take a look at the series put out by Phase4 Mobile, like Rain Sounds HQ and Rain Sounds Free before you decide. That series of ambient sound applications runs in the background, like this one (most sound apps in this genre surprisingly dont!) - so you can use an alarm clock or other app simultaneously.

Jonny0007 about Rain Sleep Sounds