Since Facebook allowed users to "subscribe" to other users, I receive a notification when certain friends update his or her status. I've checked the subscription settings of these friends, and I don't see anything different than those of non-notification friends. Does anyone know how to turn this feature on/off per friend?
If they are on your "Close Friends" list then by default you will be notified whenever they post. To turn that off, click on "Close Friends" in the left sidebar (if it is not there then click "More" next to "Lists" and then click "Close Friends"). Then click on "Notifications" at the top and choose "Off". Of course you could also remove the person from your "Close Friends" list.
Groups are the same way. If you do not want to receive notifications for posts to the group, click on the group name, then Notifications at the top of the page and choose "Off".
It was happening to me also and I have no one in my "close friends" list and had those notifications turned off. I found this online:
When one of those newsfeed updates pops up in your red flag notifications here's what you do. Click the world so you see notifications as that little drop down menu. Run your mouse over the offending notification and look for a little 'x' in the top right hand corner. When you put your mouse over the 'x' it says 'turn off'. Click the 'x' to turn off these "activity notifications."