Sound Check keeps turning on by itself
I have an iPhone 6 Plus 9.3.1 (13E238), and I've noticed that after turning Sound Check off (in Settings -> Music), it will come back on by itself after a while (maybe several weeks later?). I've had it to do this about 3-4 times now over the past several months. I do not sync my phone with iTunes. Any idea what is triggering it, and how to stop it from happening?
iPhone 6 Plus, iOS 9.3.1