If I can help it I just use: play -n synth brown on any linux system with sox installed... it's definitely the cleanest sound I've found.
Problem with most phone programs is that despite brown noise being comically easy to generate live, they record a clip and then loop it so there's weird artifacts.
I honestly don't know why I don't have the ability to run such a trivial command for an open source system on my phone. If I paid for a phone app to make noise it'd be inferior for money. I don't know why it's not at least equal for money.