I let very few apps give me notifications and disable most of them. might be worthwhile to go to notifications and turn off a few. I have only about 5 or 6 enabled beyond the ones you can't control.
I had ghost notifications from BBM and SMS (Textra) and could never find a reason, although they showed after an update. I finally did a hard reset and they disappeared. Kind of a pain to do that, but it worked.