My front SLX brake runs very free without making any great squealings when stopping. However recently when climbing standing up it has been making strange scraping noises.As you push to the right, it scrapes, push to the left and it doesn’t. Wheel is tight in dropouts, caliper is firm and recentering makes no difference, spokes appear tight. This is really puzzling me, something must be loose but what, or is it just normal spoke flex? Suggestions please.

fork flex – spoke flex would not move the disc in relation to the fork. It only needs to flex a tiny bit to scrape

Yep, fork flex, my On-One carbon forks do this. Also flex backwards quite a lot if i grab a big handfull of front brake when bedding in new pads!