After sending a video to TYPEONE and consulting with them, it seems almost certain to be a metal bearing blow. The reason the sound comes and goes depending on RPM is that the connecting rod moves according to the engine speed, and at its maximum extension (at the point of greatest swing), the piston is lightly touching the head cover.
I always knew I’d have to deal with the engine someday, but it came sooner than I expected.
The car will be transported by carrier, and they’ll check which engine parts are usable and which aren’t while doing the overhaul. However, they’re quite busy at the moment, so it looks like it will take some time.
I’m just glad this didn’t happen far from home or cause an accident when the problem occurred. I’m hoping it’ll be fixed by the end of the rainy season…
