Here is another app that really helps me with stress - It's called White Noise. It's free. It has a ton of sounds to choose from that are relaxing - Trains, chimes, grandfather clock, extreme rain pouring, oscillating fan, thunder storm, crickets, beach waves, white noise and airplane travel (ok, that one is odd).
There are a lot of free and paid versions of 'sounds', but this is a good one to get started with. I have many others and am even collecting a little library of my own nature sounds to add via a 'recorder' app.