house party laws?

Hey so I'm curious as to cops busting up house parties with a "21+ only" sign on the front door. Are they allowed to enter without a warrant and probable cause? I mean if there is no ganja being smoked or illegalities going on, just loud music and stuff, do they have the legal right to enter.
I know I have the legal right to refuse them entrance to the house if they don't have a warrant, but then that could give them probable cause to think there is something suspicious going on.

There are two reasons they would show up, noise complaint or making the rounds, but they usually stay away since there is a dead end.

Well, what do you think? Should I refuse them entrance if they request it or let them in in that situation. I'm over 21 and there is a sign that says "21+ only" but I definitely don't want cops in my house, especially with intent to search the whole thing.

if there is nothing illegal going on or in the house, let them in, but i wouldnt without a warrant anyway.

but without a warrant they can not come in unless you let them. if you do not let them and they have no warrant and they come in anyways, anything they find will be no good in court. at least where i live.

if in fact they are looking for you, and they have a witness saying they saw you go in there and you live there then they can come in and look for you without a warrant.

NO.. Do not let them in.. Desire of privacy is not probable cause!! That would be pretty circular logic if it was..
In actuality you have no idea if illegal activity is going on, but you could find yourself responsible for it if they discover anything..
There is one reason they want in that house, to hunt.. A noise complaint can be handled at the door..
Plain and simple, never let them in without a warrant, and scour the details of any warrant they hand you.. Be polite, but reserve your rights.. If you need some excuse, just say you have a friend in law school who's always going on about stuff like this, and you can kind of see their point..

all they have to do is see someone they think looks underage drinking and they will want to card everyone present. the sign on your door means nothing.

doent matter if they say go around to the front from back or garage and keep the house locked and simply tell them they cant come in and then they cant see anyone who might be underage and that you wont open the door unless they have a warrent

Opening the front door to walk out is perfectly acceptable, just make sure nothing is in plain-sight when you walk through..
Now on the matter of the sign, I'm actually not positive thats a good thing to have, because it is completely legal for underagers to be around alcohol drinkers so long as they aren't drinking themselves when there is no sign.. A cop might try to clinch that as their reason for entry if they think they see a younger person..
The technicalities on the subtle aspects will vary from place to place.. For instance, in Canada the police have alot more freedom than ppl think as far as entry into many areas that are not specifically 'dwelling areas' without a warrant on suspicion alone.. Both the narcotics control act, and the food and drug act afford them that right in many situations..