why are you shaking your phone?
Mine does it to. Type a long sentence in notes, and hold the backspace key for 2 seconds.
I'm jailbroken on 2.2, but it happened when I wasn't jailbroken on 2.0
Have you tried holding down all the physical buttons and giving it go?
none of the physical buttons
Mine rattles too. I recognized this months ago, and never really thought anything of it.
I deem it normal.
Well not to make you feel bad (in case it does), but I've ever felt any rattling since November 12th when I got my iPhone 3G.
it may be the battery, i have seen a friend strip his iphone down (fool) lol, the iphone 3g's battery is just stuck the the back plastic by some sort of double sided tape its not screwed down so that maybe the little rattle.