Hearing tests! I scored ridiculously high when I first enlisted, and my right side was slightly better. I did two years of training and then spent three more as a radio voice interceptor and analyst in Korea. Then I took another hearing test just before ETS. I usually kept my headphones over my right ear while scrolling freqs so I could hear what was going on in our bay with my left. And what happened? Right side hearing diminished below left. Yay!
When you re-take the test, close your eyes and make sure you get a good solid seal around your ears with those headphones.