Thanks for all the great replies. I didn't know it was so common. Mine is like a high pitched whine. I don't know how much it varies. It always seems to be there but at times I am not aware of it or it doesn't bother me. Sitting here by the computer with printer going and no other noise, it is quite obvious. It bothers me more at bed time in a quiet room. That's where the sound machine has definitely helped. There are times when I am not aware of it. I read somewhere that it might be stress related. It doesn't affect my enjoyment of music.

I will mention it to the doctor when I see them next time.

Clive