The adjective cacophonous describes loud, harsh sounds, like the cacophonous racket your brother and his band mates make while trying to learn how to play their instruments.
To correctly pronounce cacophonous, accent the second syllable: "cuh-CAW-fuh-nus." It is related to the Greek words kakos, meaning "bad, evil," and phone, or "voice." You may feel like you're facing something evil if you’re bombarded by the cacophonous sounds of, say, political pundits yelling at one another, or the chaotic sounds of traffic and voices on a busy urban street. Cacophonous is the opposite of harmonious.