A few years back, I had a particularly loud neighbor who had a subwoofer directly against my bedroom wall, the same wall my bed was against. The layout of the r

A few years back, I had a particularly loud neighbor who had a subwoofer directly against my bedroom wall, the same wall my bed was against. The layout of the room precluded moving the bed against any other wall. I own the predecessor to the WH1000XM3 you have, which were at the time arguably the best active noise cancelling headphones on the market in terms of the efficacy of the active noise cancelling. They did a fantastic job of covering up the sudden bass hits of the subwoofer, but when my neighbor got especially rowdy the bass could still slip through. I've worn earplugs to sleep for years, so I had some handy, and thought if the headphones weren't enough, headphones plus earplugs might be even more effective. When I tried them together, I was surprised that I could now hear the bass more clearly. I hadn't considered that active noise cancelling works by producing "anti noise" which has an identical amplitude to the noise it is trying to cancel, but an inverted phase. By wearing earplugs, I was blocking out the anti noise which was cancelling out the noise of the bass. I might as well have been wearing regular headphones over the earplugs. Since you're also using brown noise, maybe the earplugs are still providing you some benefit, but consider testing without them.