A: Sound travels much faster through water and metal than it does through air. I've heard similar loud squealing sounds, but they came from pressure regulators that were having water leak backwards through them due to thermal expansion. Do you have high water pressure and a pressure reducer? If so, do you have an expansion tank? That might help prevent the high pressure that ultimately causes the noise you describe.-- Larry (12/11/06)

A: The possible culprits: Heat trap, check valve, pressure reducer. I've had all three cause this sort of trouble. From your description, I'd place heat trap as the "most wanted". Quiet heat traps are made now. It would be nice to know what the water pressure is too.-- Larry

Q1: I have checked the installation and can find no heat traps, pressure reducers on check valves installed. Strictly a valve in the line of the water supply. Would adding heat traps cure this condition?

A1: Try turning the gas control down when you hear the noise. If once the flame (and thermal expansion) stop, the noise stops, then it is a clue that something may be restricting back flow. Is there a hot water recirc line with a check valve in it? What you describe is the sound of a mechanical part. We need to find out where that part is..-- Larry

Q2: It is electric. I suspect the inlet ball valve is causing this noise problem. I drained the house pipes again and left all faucets open, flushed toilets and opened heater pressure relief valve. I also made sure the inlet valve to the tank was fully open. Let the system stand for a few minutes then closed everything back up and opened main water valve. After all pipes were bled for air, next two showers had no hammer effect. My thought is the valve may have been slightly closed and caused the water hammer effects. I will monitor this but I am now fairly sure the trouble is in the pipes and not the water heater. (6/27/06)

Q: Lots of great information on this site, perhaps someone can help me out... Recently purchased a house, has new electric water heaters in it (less than a year old, but more than 6 months). There is a 40-gal one for just the master bathroom in the ceilng. Works great, haven't had a problem so far... Last night we heard a pop/crack/bang type sound. Not too loud. Sounded metallic. Too sharp to be duct work. Didn't sound like wood settling. Didn't give it much thought. A little while later same sound, twice in quick succession, maybe a little louder. Within half an hour same sound, much louder. Time to investigate... Was up and around trying to figure it out when we heard three extremely loud and sharp bangs in quick succession. As if a very impatient person rapped very hard on a large doorknocker. Became suspicous that it was coming from where the water heater is. I opened up the taps in the bathroom. Hot water came out, not at all scalding, but perhaps hotter than usual. Checked outside where the relief valve pipe exits the house and it was bone dry. After letting water run awhile, closed taps heard heater refilling. Didn't here anything else all night. Just prior to the whole incident two showers were taken which would have probably used up most of the water in the tank. So.... Any brilliant ideas? Haven't been able to repeat the condition. Evidence it is the water heater a bit circumstantial, but enough to make me worry about the thing leveling the whole house. Thanks in advance for anyone's wisdom! Ken

A: Do you have a check valve, back flow preventer, pressure reducer or anything else in line that may get in the way of thermal expansion? Try using a lot of hot water again and then putting a pressure gauge on the heater's drain valve. If pressure rises, there is a problem you need to find. High water pressure won't level the house, but will break the heater or some other plumbing. You may want to test the relief valve too (and be prepaired to replace it)! (4/08/05)