I figured it out! Sorta.
A friend suggested it was Amber alerts being sent to my phone. For some reason I wasn't getting any other notification other than the vibration alert.
For some reason, that worked. I reinstalled Textra and all is working again.
No more possessed, vibrating phone!
Hi there, @userHTRh1yYxt3. Thanks for posting.
When did this start to happen?
Also, can you please go to Settings>About Device and provide me with your device's model number, carrier, and Baseband version?
Mine was literally vibrating once per minute, insane. Tried turning off the smart alert after trying everything under the sun and I think that might have done the trick! It's been five minutes of vibration free silence. They should change the name to insane alert.