Constant knocking noise, rear drivers side

Long time user, first time poster!

I know "knocking noises" are prevalent in many questions but I’ve not quite found the answer to this one…

Bit of history, it’s 2002 Civic Type R. Over this weird summer, it’s basically sat on the driveway for 5 months…with the occasional start up and half mile round trip. It’s quite clear that the brakes have suffered, there’s visible rust and they grind when moving (and get hot when driving for a bit). Today, however, when I’ve gone for a little run, it’s now developed a constant knocking noise from the rear drivers side, that increases in speed as you do and vice versa. It’s not just when I accelerate, it’s also when coasting. It’s NOT quiet, it’s easily heard. Obviously, I didn’t take it particularly far, as I felt like the wheel could pop off at any moment…

I’m convinced that the brake issue, born from a lack of use, is part of the problem, but I’ve not come across this before. There doesn’t appear to be a leak anywhere, from the lack of evidence on the driveway.

Any ideas?