if they are shimano xt m775 sintered pads, then there lies the problem!
simple solution goto superstarcomponents and buy the sintered pads on there = silence!
i had stock shimano sintered and they made a constant howling/squealling horrid noise no matter what the weather/temps etc rain or dry…
i swapped to shimano resin and they were pretty much quiet, but lacked bite in the wet etc and was getting through them at a fair pace
thought sod it try sintered superstar and low and behold they are silent in all but mega snowy/ mega wet conditions, and still have most of the life left in them after 3 months of pure winter mud/grit!
seriously, i thought it was a fluke with mine, as id used the superstar ones just in the back, which i was shocked how quiet they were, so i bought another set for the front and put them in, and again total silence in all but the very wettest conditions, which proves its no fluke!
soooooo if they are sintered shimano then take out, bin and swap for superstar!