Try checking first the games you have installed, there are some games that persistently run in the background and send notifications from time to time. Also, check your microsd, there was an issue with microsd persistently being read by the media scanner, this could be what drakester09 is referring to. It's not really clear if persistent microsd scanning is the microsd's fault or the phone itself, but most reports point to Samsung devices and Sandisk microsd. I've been using both brand combo through Omnia, S1, S3, and now S5 without ever experiencing it though. Microsds used are 2GB, 8GB, 32GB, 64GB.