hydraulic brake "warbling" sound
I have 3 bikes with hydraulic brakes and each make a rather loud warbling sound on one or both of the brakes. Friends have thrown out ideas - brake pads, misalignment of some sort - but none make much sense to me. My bikes with cable disc brakes don't and never have made this noise. I wondered if it was a small amount of air in the lines but none have "mushy" braking. The brakes work well otherwise. I'm guessing this is not terribly uncommon but ?? Any help appreciated.