If you want to get involved and help resolve the situation amicably, then you will need to dig deeper into the “noise”. Is it people noise or mechanical noise? When did the noise start? What’s changed recently in the circumstances of the 2 parties? New floorcoverings? New children or other occupants? Health issues (eg, dementia)? Viagra in the water supply?
Could it be vermin? As Whale has said, getting the complainant to keep a log of events is very helpful.
Expanding on Jimmy’s comments, certain medical conditions can make people more sensitive to noise, eg, chronic pain sufferers.