You know what I'd do in that case? I'd break out the video camera, let them in, and then start planning my early retirement as a result of winning civil suits for unlawful actions by the cops. Of course the alternative is I could barricade the doors and take up a sniper position behind some sandbags. But since I KNOW I'm not going to win that one, and will probably have my house destroyed in the process...I think I'll stick with the first option.
You had better have the video running when they knock on the door because unless you record the initial exchange, you can bet the cops will tell the jury that you voluntarily allowed them into your house, and there goes your retirement fund.