Hi Mike, Id like to see that in action.In Australia we use 3/4 and 1/2 copper pipes and I assume it may be a similar situation there. I am guessing a bit/lot here, but if some of your appliances are connected to a different size pipe, possibly you are getting some kind of pressure build up. Perhaps tis is a train of thought for you to follow.Though as a scuba diver I have learned that water is not able to be compressed, so pressure build up in pipes would not be possible, unless the pipes themselves are compressed or expanded, perhaps due to temperature changes or because the shut off valve in the washing machine and dish washer work so fast that the pipes expand slightly with the water pressure coming in.I guess the easiest solution would be to turn your mains tap down so that the pressure feed is reduced.As I said this is entirely untrained/informed info, but some of it may make sense. I am sure some expert will have a better idea.
