Ah, I have something like that, only I believe in the paranoia... Well, I have come to, after having this all my life.
I get pretty much the same thing, only for me I see that sort of thing, instead of hearing it. It usually happens at least once a month, but I'll see large movements out of the corner of my eye, but when I turn to look nothing will be there. This happens mostly in either broad daylight, or when I'm in my room alone. My earliest memory of seeing things like this was when I was three, I saw something large running underneath the window I was looking out, but when I turned my head to look there was nothing there, and no where for anything to go.
Or I see things as when I fall into that state of half-asleep, I keep my eyes half open but don't really look at anything, you know? Well every now and then when I do that, I can actually see a silhouette of a person walk through the hall right past my room; right infront of my eyes. But when I get up and look there's no one there, and I'm either home alone, or no one else is upstairs/awake.
I hear things sometimes too, but it's not like yours. What I hear cannot be described... It's horrible, just inhuman screeches and such... But I only hear it when I space out and lose my focus on being, so I try to stay alert so I don't have to hear things. :3
What I see and hear scare the crap out of me 'cause I don't like the unknown. And I can't do anything about it, 'cause I have talked to spiritual people before, and they have all sorts of recommendations to curing it, but mine never last long enough for me to do anything regarding them. D:
Maybe you should see a spiritual guide? Or get your hearing checked, trust me, it's a lot easier to just have a problem with your hearing.
3nodding 
