It happened to my daughter and to my son in law in my house.
At night in their bedroom both awake they heard an old man's voice, so real that my son in law asked my daughter if she had said something. She said no. I have two grandkids, my son in law grabbed my older grandson and he said "I'm not going to let them take my son" referring to my older grandson, and he hugged him. My daughter had my youngest grandson with her. That was day before yesterday.
Yesterday 4:30 am, I was sleeping (I don't wake up easy) and I woke up because of the strong knocking (4 times) on my bedroom door. I didn't ask who it was; I realized that there was no one there. This wasn't the first time. Other times I heard a family member calling me. I lock my door to go to sleep. In all the houses I lived, it happened the same, you hear someone knocking on the door but when you go to see, nobody is there.
Not only me, sometimes we are in the living room and it happens. This is true. No kidding. It sounds so real when they call me that I ask who's there but nobody answers.
It's always my daughter or my wife calling me. I don't laugh about what I don't understand but there are things that exist even when we can't understand.