It would be a shame for anyone to feel they couldn’t post. But it is important to keep topics (mostly) on-topic, because forum conversations are long-lived, and organised by category and title, and that’s how people find what they’re looking for, and avoid what they’re not.
If members want to reply but are concerned they might be off-topic, simply reply as a new linked topic instead.
In the aircraft noise topic, Snazy asked what other noises bothered people; but then I think he realised this might take the topic off-course, so he created a new topic to discuss other noises. This new topic was popular, and the aircraft noise topic stayed on-track. All good
The “noises that bother you” topic stayed on track, but the reason I brought it up earlier is because the topic creator responded personally to a lot of the replies, which is a nice friendly thing to do (and is what you’d expect if the topic were a blog post), but on a forum post, this is unnecessary, IMO, if these replies don’t add any new info. It’s a signal / noise ratio thing.