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.

[added]
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?