Talk about being at one's wits ends, we are awoken every night, mostly around 2-3AM with a loud, piercing squeal coming from our water pipes. The only relief we can get is to leave the hot water running. A small drip from one of the sinks usually would calm the noise, but now we've had to leave one sink on "full blast" to relieve the noise.

Note, we've never heard the noise during the daytime and it comes no matter what the outside temperature. Any help would be greatly appreciated.

Use process of elimination.

Tonight turn off water to the house by closing the main valve.

If no noise tonight, leave main valve open tomorrow night and close the cold water input valve on the water heater.

Look to hear from you in two days.

Knocking, popping, creaking, cracking and strange noises are a common complaint, especially in colder weather and at night. I can tell you what's happening and take the mystery out of it but you're not going to like the repair. When a draw is made on a hot water line the line expands against a pipe strap next to a stud and when you drain hot water from your tub or shower it goes into a chase that is a little cooler then room temperature. The heat expands the pipe causing it to rub against the stud to which it is pipe strapped. This is the sound you hear. As it cools it contracts and the noise is heard again. To repair it you must tear open the walls and locate the pipe strap that's causing the problem and shim it tight. Most people when they learn what causes it just elect to live with it. Good luck and thank you for rating my answer. Tom

Do you have a water softener? Is the sound happening when it regenerates? Most softeners are set to regenerate around that time.