Where does the buzzing sound come from?

Background: Mrs. Lee’s son is 14 years old. He keeps hearing buzzing/hissing sound for a few weeks. Mrs. Lee is concerned if her son has tinnitus.

(1) What is tinnitus? Where does the buzzing/hissing sound come from?

(2) What treatments are available?

(3) How can we prevent tinnitus? (FindDoc Medical information)