Noise Crush is Shade Man's power. It sends a sound wave to damage enemies. To charge it up, bounce a wave off a wall back at yourself. It will do more damage to enemies.
Warning: Do NOT try to use the Noise Crush against Shade Man. He'll just absorb the sound wave and shoot it back stronger. Too bad you can't do the same to his.
Fun facts
The Noise Crush is spelled Crash Noise in Mega Man: The Power Battle, and Crush Noise in Mega Man 2: The Power Fighters.