Have you ever heard voices that weren't really there?

This is what happens with me exactly. Although it hasnt' happened as much recently, I can remember such occurances throughout my life span. It's insane to think that so many people hear voices/see images that so many other people don't. Perhaps it's a perception factor more than someone being "crazy". Don't get me wrong - some ARE crazy but simply seeing/hearing something that others don't shouldn't be the only symptom. I once lived in a house where I was constantly seeing the same image - that no one else noticed. A friend of mine also saw an image repeatedly that no one else seemed to notice. We didn't see the same things but at the time were questioning our sanity on such facts.