I started getting a high pitched ringing in my ears after having a cold just over a year ago. I visited my Doctor a few times but nothing cleared the ringing. In the end I was sent to a hearing specialist, I was given a test where you have to press a button when you hear a sound. After this he told me that I had permanent hearing loss in the high frequencies, this occurs when the little hairs in the ear are damaged (they think they are hearing something when they are not). Not working in a noisy environment this was a shock to me, but as time goes by you sort of block it out, it's at its worse when it is really quiet.