Why don’t you ask the wife if she’s ok next time you see her? You have no proof she’s being abused. A loud thud could be anything through a wall. I hear thuds through the wall of my neighbors all the time. I hear them shutting cabinets and running up the stairs. Unless you hear her screaming or crying, or you actually see the abuse, you don’t really know. Just because he yelled at her once, doesn’t mean he hit her. Ask her if she’s ok, and find out.