Mine changes daily--starts out as a loud ringing in the left ear when I wake up--last night it was so loud it woke me up. Then after I'm up for a couple of hours it softens. I don't know if it's from the Xanax softening it or not. I'm tempted this weekend to not take the morning dose just to see.... In the mid morning it either gets lower or it starts a kind of whining sound in the left side of my head. I too, sometimes get the hissing.
Maybe all this is normal. It happens most days. Sometimes, when I'm really lucky I get a very low squealing or twinkling type sound all day. That only happens once or twice a week--one time it happened three times-but that hasn't happened again.