Noisy hot water pipes when using water

Help! It sounds like the hot water pipes in my home are going to bang themselves apart! When hot water is running to any faucet in the house there is a constant rythmic banging through all the pipes in the house. This includes the washer and dishwasher although I can't say for sure if the shower causes it. I can even hear it banging under the house where the main line comes in.

This is a new problem that started after we used the hot water tap behind the washing machine to fill a backyard pool for the kids. We had a hose hooked to the line and opened the valve until no hot water was left then we closed it until hot water recovered and then repeated the process. When I hooked the washer back up and turned it on, the banging began. Only happens when water is flowing through the hot water system.

Does anyone have any idea what may have happened to our plumbing and how to fix?

noise

Take that hot valve apart that you used for outside and look to see if the washer is off or loose or is warn badly. If it is then fix it or replace it.