My wife and I have a new two-level condo unit. Whenever we use hot water in the shower or bathroom sink on the upper level, we hear a knocking noise from the pipes. (Actually, I now refer to the noise as the "kettle noise" because I decided it's similar to the popping noise you hear from a tea kettle when the water is just starting to boil.) The noise is usually less during the day and at its worst during the early morning and at night. (One plumber said that may be because these are times of the day when more people in the area are using water.) We've had a plumber come to our home, cut open the ceiling from the lower lever and strap down the pipes. I've turned down the water temperature in the hot water heater. The noise however continues. Does anyone have a clue??? Please help.
Since you notice more noise at off peak time I would try lowering your incoming water pressure or lower the pressure off your hot water source.
It sounds to me as though youre hearing the expansion of the "cool" hot water pipes as the hot water makes its way to your upstairs bathroom....very common and obviously louder in the morning and evening as the piping has not been used and is at its coolest. Again very common whatever the age of the structure. Not too much you can do about it after the fact....The way to handle this at the time of construction is to use heavy foam insulation on all the hot water pipes to lessen the noise, personally I would insulate the cold as well to reduce the noise from the cold water between floors....This is plumbing 101 course "simple expansion and contraction". erik