Help Rainstorm sounds when I plug in

[RakSiam]

I've had my MotoX for quite a while. A few days ago it started doing something very strange. When I plug it in to charge via the wall charger it starts playing rainstorm sounds...like a white noise generator. I have never installed any white noise apps. So I can't figure out where the sound is coming from. I can't find any sort of settings to disable this. It is baffling. I have Android 6.0. Any idea how I might be able to figure out what app is making this happen.