Try booting into Safe Mode (instructions are at the bottom of that article I linked in the previous post). This disables all 3rd party apps. If the problem goes away, then something you installed is causing problems--the tricky thing is trying pinpoint which app. You may just have to uninstall apps one by one until the problem resolves. If the problem persists in Safe Mode, then there may be something wrong with the system software/firmware. Did this behavior start after a system update? If so, try talking to Samsung, since it should be their responsibility if an update they sent out causes problems with your phone.