Random vibrations

Heres something that just started yesterday.
My phone will randomly vibrate.. even when the screen is off and locked.

Not sure whats going on here... there are no new notifications.. nothing.. just randomly there will be a single short burst vibration.

Phone is stock, unrooted GB.
It's a CLNR that I just got about a week ago and this issue was not present until yesterday.

Anybody else have this going on with their phone?

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