At the end of the 1983 "Hawkeye" 4-issue miniseries (seriously it's so great, read it if you get the chance), Hawkeye and Mockingbird get captured by the the Death Throws (best villain team ever). Crossfire, the leader, has a plan to kill the Avengers by first killing Hawkeye, and then getting all the other heroes when they come to his funeral (because Crossfire is shitty person). He plans to accomplish both of these with a brainwashing machine that just makes people go batshit insane and try to kill everything around them.
So he turns it on, and Hawkeye and Mockingbird go ballistic and start beating the shit out of each other. Crossfire is a twat, so he stops it for a bit just to let them come to their senses enough to see what they are doing, before starting it back up again. But while it was stopped, Hawkeye had slipped a sonic arrowhead into his mouth - when activated, it nullified the effects of the machine long enough for him to regain control, but of course it blasted out his eardrums. He's then able to KO Mockingbird safely (because she's still crazy), and defeat Crossfire. Mockingbird is the one who later gets him hearing aids and helps him adjust to being deaf.
When he was reborn after House of M post-Franklinverse, he didn't have the damaged eardrums, and therefore was no longer deaf. But then in Fraction's Hawkeye, he got stabbed in the eardrums by a psychopathic clown and is deaf again.
