Not sure I’ve had the combination of rotor, wheel, fork and calliper on the bike (Swift) before.

Swapped out a 29r suspension fork for the original rigid fork.
Shimano rotor, SLX calliper, 160-180 adaptor in place.

When tightens everything up, it’s as if the rotor (jagged) is catching/rubbing on the retaining spring (rather than the sound you get from just rubbing on the pads).

Is a washer the preferred solution, or can you bend the spring to a more square profile – or try and find a slightly different adaptor that pulls the calliper a bit further out.

I’ve used a couple of the thin washers between caliper and adaptor to get better pad alignment, coincidentally also on a rigid fork, so crack on if need be I say…

I’d take a guess and say the mount isn’t quite as accurately placed on a welded fork over a cast lower.

I also had to get the mounts faced come to think of it to get rid of brake squeal when I first got them.

I’ll look again at the mount and adaptor / calliper area.

The weird thing is, I’ve had the same forks on the bike most of the time I’ve had it – from new, 3+ years ago – only swapped in the suspension forks as a stop gap in May. I think the calliper is a new SLX. I’ll try the original 27.5+ wheel (with rotor) and see if there its any difference, but I’ll try a couple of thin washers as well. And make sure the wheel is bedded firmly (!)

The caliper isn’t just misaligned due to a lazy piston is it? Can make a similar noise to catching the spring of it’s just catching the caliper body I’ve found. Have a look to see if the rotor is dead centre of the slot in the caliper or see if one piston is out more than the other.

Good shout. Not going to faff about any more tonight but I’ll def report back.
Will also try leaving out the spring for the test, and swapping for new pads anyway – the (resin, I think) ones that came with the brakes look a bit worn (though not ground right down).

cheers.

Sounds like a problem I’ve been having with Deore 615s. Try bending the spring. That reduced the problem for me. But I suspect that your pads are fairly well worn, resulting in a lack of clearance between the spring and the rotor, so new pads will probably fix it.

Bending the spring helped a bit.
Daylight helps as well – really hard to see what is catching when it’s all a bit gloomy and it’s the end of the day.

It does appear that the inner piston is being a bit rubbish / lazy – hard to tell if it retracts at all, if so not very much. Will need a bleed of the brake and see if that spices it up. Pad has some wear but piston looks to be main culprit. thanks @survivor.