if I do the old trick of rubbing wet mud/sand on the rotor, ride for 5 minutes the noise stops. Rest of the ride is in lovely peace and quiet.

Next ride, the same thing, need to stop and rub mud on.

Why isn’t rotor cleaner working?

Because its not dirty – glazed pads it sounds like to me – the mud rubs some of the glaze off to stop it.

Sand the surface of the pads and bed in again

could also be contaminated pads – the mud scrapes the surface contamination out but after awhile it seeps thru

Could also be leaking piston seals

You should only need to clean the rotors if contaminated

My pads do this – seemingly after a big descent, so as TJ says could be glazing over. Dunk in peat/mud/crap and ride sorts.

I thought about the pads being glazed, however I can’t understand how the noise comes back next ride if I had scraped the surface clean.

Leaky piston seals might be the culprit. Will be annoying (and expensive) if it is – xtr trails….

My tip – stop using rotor cleaner. Totally unnecessary and more likely to make your brakes squeal.

would i be right in thinking shimano brakes ?

xtr trails….

would i be right in thinking shimano brakes ?

Top investigative skills 😉

ah missed that tagged on the end

my moneys on weaping piston seals.

leaky pistons – well it was for me…

change the pads and see if it comes back.

Once again TandemJeremy is correct

Sand the pads as they sound glazed

My money is on English lessons, they’re called BRAKES. 🙄
Breaking is what they do just before they’re broken FFS.