Raucous means unpleasantly loud, or behaving in a noisy and disorderly way. It can be hard to give an oral report in the front of a classroom when the kids in the back are being raucous.
Raucous is often used to refer to loud laughter, loud voices, or a loud party, all of which can be harsh or unpleasant. Near synonyms are strident and rowdy. This adjective is from Latin raucus "hoarse." Think of raucous as people whose hoarseness can't come on too soon.