2 bikes are sram hydraulics. the mountain bike is very old and not sure; it's hanging on my garage ceiling at the moment.
it's definitely not screeching - that happens with moisture on all my disc brakes, hydraulic or cable. hard to believe that all 3 of the bikes that are hydraulic are doing this and my cable actuated are not - contamination would be equally likely on all of the bikes.
I'm going to try to record the sound. my newest (sram axs xplr gravel) is the loudest.