Why won't my iPhone 4 vibrate when it's locked?

Under settings, I already switched "Vibrate on Ring" on and "Vibrate on Silent" on. However, my phone doesn't vibrate when it is switched to silent and the phone is locked. It vibrates if I'm using the phone when I get a text, but not when it is locked. I have ringtones and vibrations set for calls and texts. But nothing happens when it is locked.

  • Why is my iPhone 4's Vibrate SUPER loud? So I have an iPhone 4 that I got from Craigslist. I've had it for awhile now, and the vibrate is SUPER loud. I purchased a new vibrate for it, but it's still loud. I have to have it on silent in school, otherwise everyone can hear it. It really annoys me. Is there anything I can do?
  • Why doesn't my iPhone vibrate? I have an iPhone 4S and I got it in July. For some reason, it doesn't vibrate! When I go to the settings to just set a vibrate tone it doesn't vibrate. It never vibrates, and I think it used to. Is there anything I can do?
  • Why doesn't my Iphone vibrate when I get a Text? I always have it on Vibrate but it just stoped vibrating. And now when i get a text the screen doesn't even turn on i have to turn it on to see.
  • Why does my iphone randomly vibrate? I got the iphone 4s less than 4 weeks ago in america on Holiday, a few days later ios 5.1.1 update came out so I downloaded it. I've been home almost 2 weeks now and for the last few days it has been vibrating when charging, its really annoying, it seems to happen most when i'm using an app which is not so good for me as i'm trying to get my high score on temple run (currently 2 million).so any advice would be helpfull, anyone else had this issue?