Found the definitive cause of the remaining rattle, it
is a loose exhaust manifold heatshield. Bolts are completely jammed into the manifold though, so new plan - find a new exhaust manifold (anyone got experience with after-market ones?), flexi-pipe & cat (which I've found has a hairline fracture at the back, see below

). So much for the cosmetic bits on the car, grr!
Excellent, hairline fracture!