Why would the police knock on my door at 4am?
Why would the police knock on my door at 4am? 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.
Should you answer if the police knock?
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.