The basics are an old gramophone or something that plays music constantly, and while listening to it a faint ringing sound can be heard. After listening to it this ringing persists and gets louder and louder. Much like a strong headache, this will reach the point where it is incapacitating for the subject.
After an amount of time (I'm not sure if hours or days) this will rapidly fade, and the subject will begin to hear voices. Not a single voice, but like being in a room full of people. This starts off faint, leading to paranoia and anxiety, but gradually grows louder and more violent in terms of tone of voice, leading to psychosis, self harm, suicidal and homicidal tendencies and insanity. At this point the subject will try desperately to kill himself/herself and many others to rid themselves of the voices.
That's just the basic idea, I will add other things if it gets off the ground. Let me know what you think.