vibration alert

[rob hilleary]

I keep getting this vibration alert: long (pause) short short short. Sometimes it seems to signal that an app is about to crash, usually with video media. But it also sounds off several times when phone is booting up. And lately, this same alert vibration goes off at random times when the phone is idle, or I'm on the internet but not doing anything particularly taxing to the CPU, and nothing happens (!?) What is this annoying alert?