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Check if the same occurs in safe mode:
http://talk.sonymobile.com/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008
Hi,
I've tried that and it doesn't seem to be an application that's causing the problem, cause when I pull off my case for example it may also vibrate again. I've been having this issue for a couple of days now and can't figure out what's causing this problem.
This worked for me, thanks 
Great.
I am sorry,but keep us updated.