ISM (3.82) vibrates at 5am; like an alarm, despite having none configured

4 mornings in a row now I've been woken up at 5am on the nose, as the ISM buzzes / vibrates.  I have no alarms set.  I just went in an created an alarm, then disabled it, in hopes that'll "reset" a phantom alarm that might have been set.  I actually don't know for sure what an alarm vibrate feels like, but this feel similar to when I first put on the ISM at night -- the vibration that let's you know it's awake and recording.  Could it be the reading drops/reconnects and it's notifying me?   Perhaps, but highly doubtful given the precision of timing.

I haven't been able to fall back asleep these days, so it's starting to take a toll.

Has anyone else experienced this?