Why does my iPhone vibrate 2 times while starting up?

I didn't do any after I started it up. It just started.

Added (1). It just started happening. What I mean by start up is when it does it when the white apple logo appears.

Added (2). Before it started happening I have already did disabled vibrate on ring.

Added (3). My ios is iOS 6.1.3 (latest version)

Added (4). My ios is iOS 6.1.3 (latest version)

Added (5). I think I have a curus because everything I type in safari's URL is deleted but, I am not doing it.

Added (6). I think I have a virus because everything typed in safari's url is deleted.

Its glitchy

you might have it on vibrate in the ringtones section.

I wouldn't worry about it. My LG phone vibrates once on startup or shutdown. It's just part of the sequence that the phone goes through.

Has Apple updated its software? That may have changed the startup sequence. Do you have any friends with the same phone? Do theirs do the same thing?