Other threads point to similar issues but not the same problem I have. I've been troubleshooting a lot, but can't narrow it down much. What I know so far:
- Appears random. Not a particular time, battery level etc
- No notifications appear in the bar. It can happen even when I'm looking at the phone and there is no visual indicator.
- I have a Pebble watch, so most notifications can and do come through to the watch - no notifications on it when the vibrate happens.
- It also doesn't seem to be any kind of dropped Bluetooth connection with my Pebble, as the Pebble doesn't notify of a lost connection like it normally would.
- I have also read threads for other HTC phones where it pointed to nfc being switched on. While I do usually leave NFC on, the vibrate still happens even when I disabled NFC
I was holding off until Vodafone decide to release the Sense 6 update, but I'm not holding my breath there...
Is there anything that I could investigate? I was trying to avoid rooting or modding the phone for as long possible, but would be prepared to do it. However, I don't really fancy going down that road if the problem will still be there.