Do police have the right to enter and search a house because of a noise complaint and beer cans in the yard?

my friend (in PA) had a party and the cops came because of a noise complaint. there was beer in the backyard along with underage kids who were drinking and playing beer pong. the police then came into the house and searched everywhere for illegal substances and other kids on different floors. I understand the kids outside getting in trouble, but do the police not need a search warrant in that kind of situation?