iPhone plays “Xylophone” ringtone for no reason

Also, most of those things I would think would make the screen come on or vibrate the phone, but my screen just stays black while it happens. If I tap the screen to unlock it it behaves normally as if the sound isn’t playing and my face or code unlocks the screen lock but everything still looks normal on the screen. No badges, banners or icons of any kind.

So it happened again today. On a plane, in flight mode, not connected to the internet. 5 times over 20 minutes at irregular intervals. Phone was in my pocket. The xylophone was full loud volume. I turned the ringer volume all the way left to turn it down becuauae the volume buttons didn’t affect this sound, but each time the xylophone tone was at full volume. Nothing appearing in the menu bar, no vibration, no alerts, screen just black until I opened it to check everything but it was as if nothing was happening. Just 5 repeats of it 5 times until I had to just power down the phone fully to avoid embarrassment. I’ve put up with this for years and nobody has a fix.

Thanks for the reply.

1. No. Never have
2. No. Never have
3. Not that I have seen but will check next time.
4. It is off as it always has been. Sound is defaulted to Chord anyway.