So, attacked the rear brakes of the TT at the weekend, both sides seem to slide freely, and whilst the discs were worse for wear, there was no obvious scoring from a trapped stone or suchlike. The dust shield at the back was still in decent condition and not rubbing.
Back to square one on the random scraping/rubbing noise.
Drove the car less than a mile to Sainsbury’s and noticed a very similar noise whilst going over the speed bumps and the car wasn’t warmed up fully (as previously the noise was only apparent after warming up). Got home and back on the ramps, crawled underneath and had a good old rummage, turns out when the exhaust is fully warm, it moves aft around half an inch (is this expansion due to heat, or is the whole engine moving rearwards on its mounts when warm?) and as a result was fouling the rear subframe ever so slightly, when turning right, the centrifugal (centripetal?) force would have been pulling the exhaust away from this point on the subframe.
So I undid all of the exhaust joints and rejigged it so that the bend in the exhaust was further toward the front of the car by around 0.75”. Hopefully this will mean the noise is gone.
Time to go for a drive and find out!