I've got a problem with water hammer coming through a shared water main from my neighbour's house when their washing machine fills. This results in a loud thudding sound in the wall between my bedroom and bathroom (I'm guessing there's loose pipework from my shower). After a few years of negotiations with their landlord I finally managed to get them to fit a water hammer arrestor. However, it only seems to have stopped the thud that happens when the valve closes. Is there anything that can be done to stop the thud from the valve opening? I realise that securing the pipe work would be the best option but this would involve knocking holes in walls and I don't have the funds to tidy that up!