Sorry, it's a colloquialism, it doesn't mean to literally 'scrub' it.
I think I was the first person to complain of this noise back in January. For months it bugged me trying to find and solve it. Always at the same rpm 5400-5600. Sometimes gone, but usually there for around 80% of the time. Really annoying. Certainly doesn't sound like it's coming from the chain area. I even stuck clothe under the dashboard in February, but nope. It really does sound like it's coming from the top of the engine. The same as everyone else is now complaining about.
First time I properly cleaned the chain with a proper chain cleaner, and lubed it with a proper o-ring lube it completely vanished for a few hundred km. And has done so ever since, never returning for a long time afterwards. Which is amazing as the noise isn't coming from there.
Massive coincidence if so many other people have the same noise at the same rpm and it's something entirely different.
Strange that with all the experts that no one has found it yet. I mean the top of the engine isn't exactly massive.