How can I determine what is causing my iPhone to buzz? I recently got an iPhone 4 (with iOS5). I almost never have the ringer on, so the phone is mute and alerts (like incoming calls) come with a buzz. Periodically, while the phone is idle and no call in coming, the phone buzzes. I figure this results from some notification, however no recent notification shows up in the notification finder, nor have I recently received any emails. 

How can I figure out what is causing these alerts?
Go to Settings->Notifications on your iPhone and then look in the section Not In Notification Center. If there are any apps listed there, you can see if notification is turned on or off for them. If any are turned on, you can turn them off one by one to see which one is trying to get your attention.

You may also be able to see badge numbers changing on one of your apps which would be a clue that there might be a notification too.