Random Vibrations Hidden Widgets

Every once in a while, I noticed that the N8 would vibrate randomly and I would open up the applications that are active and there was nothing I could see causing the vibrations. The usual times I can think of when the phone could vibrate is when

• Missed call / Message 
• GPS walk mode when it wants to tell you to turn a corner 
• Gmail when new mail comes in

However, none of those scenarios occurred. It turns out that although I deleted the Email widget from my home screen, it was still working in the background (but not showing up as an active application) downloading emails and when it did, it would vibrate to let me know. 

So, your problem may be caused by a widget that is still downloading stuff long after it was removed from the home screen. Hope this helps.