William developed tinnitus (ringing in the ears) during the filming of the episode "Arena" from the original "Star Trek" series. In the opening scene, he and Leonard Nimoy are running from bombardment by a hostile alien force. One of the explosive charges detonated a few feet from him. He rolled away from the blast, as can be seen in the footage.
He did not appear to suffer any serious injuries, but over time, he developed the constant ringing in the ears known as tinnitus. The condition is often caused by extremely loud noises, such as explosions or very loud music (i.e., rock concerts).