Vibrator broke
my iphone 4's vibrator sounds scratchy
iPhone 4, iOS 6.1
There are two small screws which hold the vibrate motor in place. They may possibly just be loose. At my Apple Store the Genius for free will simply tighten these two screws. Make Genius reservation and take to Apple Store and ask Genius to tighten the vibrate motor screws. If no luck with your Apple Store, the Vibrate Motor is the easiest part in the iPhone to tighten or replace.