Help My phone has developed the shakes

[markdoc]

This morning at 6:30, my phone started vibrating. No sound, just vibration. It lasted for about 15 - 20 seconds then stopped. The problem is I don't know why. No alarms set and my phone settings had all volumes at full except music at half. Vibration was turned on for Ringer, but I didn't get a phone call.(and the ringer was at full volume anyway) Does anyone know how I can figure out what caused this to happen. It isn't the first time and it's driving me crazy. Any thoughts would be appreciated.

Thanks,

markdoc

 

[MrDangerous]

Ninjas...

 

[CrackedLCD]

It was vibrating continuously for 15-20 seconds? I have honestly never heard of a phone doing that. Very strange.