Trust me, it's not the copper. It only does it when things are draining. Like, when the dishwasher drains it's hot water. Or, if I fill a sink with hot water, and then pull the plug. A little while after the drain begins to have hot water flow down it... it begins to knock inside the wall. I have a general idea of where it is. Any idea why this would be happening, what he dangers of letting it go on, and if there is an easy fix for it?

I have only owned the house since November, and it has done it ever since we owned it. I know about expanding copper, and water hammer. Trust me, this is not that.

You are most likely hearing pipe expending in the wall. It may be that your drain is too tight against framing producing friction noise when hot water is present.

You are most likely hearing pipe expending in the wall. It may be that your drain is too tight against framing producing friction noise when hot water is present.

Could this present a greater problem if unaddressed?

Knocking, popping, creaking and crackling pipes are a common complaint, especially in colder weather. 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

Could this present a greater problem if unaddressed?

I don't think it should present a problem. PVC and ABS drains are tested before approved by local Plumbing Codes. Therefore I would not worry too much about them...

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