I find several reasons why pipes rattle. The most common is that the washer in the faucet or valve is loose. Another is that the pipe is touching another pipe or hard surface in the wall (OUCH!). And for hot water rattles, the energy saving nipples that screw in the top of the water heater, sometimes make a serious rattling noise when you turn on any hot water tap. They have a ball in them that acts like a check valve. Under a DWM it could be that the soft copper water supply is hitting a hard surface or the machine itself is not tight in the opening and is jumping around.