The Pounding Outside. . .

Have you ever lived close to an Orthodox church? I hadn't either until we move to Romania for three months. It is Easter week here. A couple of days ago I noticed some pounding that I thought was some construction workers until I started hearing the same rhythm over, and over, and over again. Obviously there is some reason for it, but I haven't been able to figure it out yet. Maybe somebody here knows. Video below shows the short snapshot of what they are doing. Let me know if you can give me the reason for this.