That has been the true reason why spirits knock in threes, scratch in threes or do anything in threes. Also, that's the reason why many things happen in threes and so many incidents, and events occur during 1:00-4:00 rather it be a.m. or p.m. Demons mock the trinity. The number seven has some significance to demons as well. Often times they have seven different forms to mock the seven hollies.
In my house, the ghosts go indeed most active. During this time, there are rooms we cannot enter and we have to have the lights on all night. I have discovered the spirits tend to target people in the dark. So in order to get any sleep in our house, we have to turn on some lights in the room we are sleeping in. I dislike the feeling of not being able to awake from dream, being pinned down or being randomly attacked.
The spirits in our house during the witching hour does anything they can to annoy everyone. They manifest, walk around, hit and knock on things, summon more spirits and have meetings. Yes, I have actually seen and heard them having like little town meetings several times. I try to listen to what they're saying, but for some reason, you cannot make out what they're saying. This is usually demonic though. Maybe it's some strange demon language.