Sometimes the phone won't vibrate in the silent mode when an alarm goes off, whether it be a calendar event or a simpe alarm. It doesn't happen always, but more often than not and it's annoying.

I've checked the sound settings and everything is ok there (i.e. vibrate is 'on' in silent mode). I thought it was the app Profiles that caused this so I disabled it, but it still happens.

Has anyone else experienced this? Any ideas of apps that could cause this?