The hissing sound you hear is an abnormal subjective ear noise that is known as tinnitus.
Tinnitus is a symptoms of an underlying condition that can affected the ear structures and ear nerve, brain, blood vessels, or it could be a sign of hearing damage due to exposure to loud noises or a side effect of some medicines.
I guess you were tested for possible hearing loss and for TMJ (jaw joint disorder with tinnitus as one of the symptoms).
Since, you feel pulsating pain along with the tinnitus, you could talk with your physician to be checked for aneurysm (blood vessel widening) that can give tinnitus as a symptom.
Another cause, that is also more serious, is a tumor of hearing nerve, but, this is usually manifested with hearing loss as a first symptom.

Best wishes!
Marija