Yes he was. As i mentioned before, Apoo's attack wasn't working on the group on this picture
> If you notice, Apoo launched his attack, visible with the "Boom" effect, and him getting annoyed("Tch") it failed
> Killer is in the same area as them, but he didn't need to cover his ears
And yes, Killer was in Apoo's range when he was attempting to attack them
Yet, Killer told them to block their ears without needing to do so himself. Putting 2 and 2 together, and it's pretty evident it implies he can somehow manage to ignore the sound, most likely due to his helmet