The police may knock and announce their presence at your door but, unless they have a warrant, you are not required to open the door, to answer any questions, or to cooperate with the police in any fashion.
People Also Ask
There could be a multitude of reasons. You could have an active warrant they are trying to serve or have possible footage on a camera at your house they need for an investigation. They could also just be trying to make a consensual contact to build a relationship in the community.
Just because it's 4am doesn't mean the warrant isn't valid or they should come back when it's convenient for you. If it's 4am and they are serving a warrant, it's because the warrant is for something important, and they want to get you at a time when you are less likely to dodge it.