Dr. Beebenson, PhD HA, ST, Offset (hons)
It's a weird thing - I never have any problems at You Yangs (granitic sand), but when I ride high-country (clay) I do get the same squeaky high pitched turkey warble building up as the day goes along. Get home after the trip, lightly touch up the pads with a bit of emery or a kitchen scourer or something and back to no problems for months of riding at Youies again. Honestly never been sure if it's the extra elevation/track length up high country or some kind of contamination from the clay dust/mud.I also run the Hope metal pads, it's not quite a wet Avid turkey warble but a persistent squeal under all conditions. More pressure, wet conditions, constant cleaning, dust, piston realignment, COVID-19 - nothing changes the squeak/squeal. I've had great success with the Swiss Stop products on XTR and Saint brakes so with any luck that will solve it. It seems to be a reasonably common complaint with the Hope brakes over on MTBR.