Loop earplugs, buy the one named quiet, it blocks over 21 decibels 👍🏼 also: come on. Try harder. Just hire some qualified person and break the damn wall and use proper equipment to understand the noise - or do it yourself, it's your wife and your life. It didn't have to get this bad, really. Also, if you're into spooky stuff: maybe the widow killed her husband a la Edgar Allan Poe and he's behind the wall and some health apparatus is emitting the noise. Who knows, right?