Re: Plumbing groaning
It's not likely to have anything to do with the vent/drain pipes but rather the water supply.
If the sound is similar to a horn sound this may be a problem with a diaphram inside the ballcock ( fill valve ) in a toilet.
This is usually a sympathetic vibration caused by water passing by a seal causing it to vibrate.
A moaning or groaning sound could be from a faulty seal in a shutoff valve , if you have a pressure relief valve on the main water supply pipe check to see if the sound originates there also check the water pressure to ensure it's not above 65 psi or not less than 35 psi.
Just a thought.
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