Yes, a plumber can fix water hammer. Water hammer is a common plumbing issue that occurs when water suddenly stops or changes direction in the pipes, causing a loud banging noise.  This can result from high water pressure, quick closing valves, such as those in washing machines or dishwashers, or from loose unsecured pipework in the wall.  Ways in which plumbers fix these issues include reducing water pressure, installing water hammer arrestors and securing loose pipework where accessible.