I base this on my own personal experiences with auditory hallusinations: I believe it has a lot to do with stress, diet perhapse, drug use, and over all state of mind. I didnt do drugs when i had them but i ate very poorly, was stressed and even depressed. I would hear things like video game sounds or instant message bells ringing. I wouldnt worry about it unless it gets worse, turns into scitzofrenia, or frightens you. I think of them as somthing like having a pictographic memory but instead of seeing pictures when you recall a memory you recall a sound the same way you heard it. As i think about it i think it was mainly due to sleep deprivation and high exposure to certain sounds.