As a LBS mechanic I won’t have sram on my bikes, appalling stuff. Mainly from Elixir days, but not seen enough of the guides yet to convince me otherwise.
Had one dodgy Shimano XT rear calliper a couple of years back that I stripped and found a nicked piston seal. Replaced that and then fault free from then onwards. Got a pair of SLX and XTR trail on my bikes currently and I don’t see me changing that. Fault free, oodles of power and silent (unless soaking wet of course).
Regarding noises, make sure the calliper is aligned to the disc properly, so both pads contact equally. Also, have you checked the calliper mounts are true? I still see a lot of bikes that need the mounts facing to make them true.