Before you do this you can back up all your text messages with this app: https://play.google.com/store/apps/details?id=com.riteshsahu.SMSBackupRestore&hl=en I do this all the time, you can easily restore them when you're back up and ready.
I have this as well. It may have something to do with ascending ringtone being enabled by default, and no way to disable it. Basically the ring starts with very low volume, and the volume increases as the tone plays. Makes sense for contact ringtones, but short notification tones are impossible to hear.
I've been looking for solutions to this without success. Maybe an Xposed module similar to this one exists, but it means rooting the phone, and Xposed is known to cause instability issues.
> https://play.google.com/store/apps/details?id=com.riteshsahu.SMSBackupRestore&hl=en
Hands down one of my favourite apps, I've been using it for a year or so and it has seen me through multiple factory resets/loaner phones!