It's called hypnogogia (or hypnopompia when you're just waking up). They're hallucinations people experience on the verge of sleep or wakefulness. They can be in the form of: twitching awake (feeling like you're falling); auditory; visual; or tactile hallucinations.
They're absolutely normal and nothing to worry about at all. In my experience they occur more frequently during times of stress. I don't get visual hallucinations, rather if I am really, really tired or stressed, when I close my eyes to sleep my brain fills up with completely unjointed words and phrases that spiral out of control. When I was REALLY anxious the same thing happened but in front of my eyes with strange shapes and images popping up and disappearing rapidly and continuously. Moreover, I have had actual auditory hallucinations in these states where I have thought someone has actually spoken to me out loud.
A good tool I use to distract myself if its freaking you out is to listen to the radio. I find this gives my mind something to train on. I'm not sure this will work for you, however, as yours are visual. My girlfriend has visual hypnogogic hallucinations and she finds sleeping with the TV on mute gets rid of them.
Just to be absolutely clear: hypnogogic and hypnopompic hallucinations are incredibly common (like a vast, vast minority of people experience them regularly and a majority of people will experience them on occasion). Moreover, they are more likely to occur, in my experience (i.e. my own personal experience and speaking with my girlfriend), when you are overly tired or stressed.
Just read 0115's reply - it could be static too. Either way, very common and nothing to be concerned about.