Hard compound -lot's-o-stuff. Your description just sounds like a hard compound combined with the notion that there are a number of forces that "retract" the pads away from the disc once they have been applied - the vast majority of brakes around will drag until you've used them, discs for slightly different reasons than drums, but I'm unsure what you are saying. You are shocked that disc brakes that ordinarily will drag due to being sandwiched right up against a disc that need vary only say 0.0001" either way could make a squeal or chatter while turning them over on an stand?
This should be totally normal... It becomes almost absurd the complexities of how such simple devices work, but as an example, what do you think when one is speaking about high performance brakes such as a race car, one does on the parade lap other than put heat in the tires and wave to fans? Ride the sh1t out of the brakes - there's good reason for this too...
After much surmising about squealing brakes, I wonder why it is that I can produce a loud squeal from the front disc/s without touching the brake lever, and a wheel speed of about 2 rpm?
Bear in mind that I have to 'play' the wheel. The squeal will start at 'a' point of rotation and will continue as long as the same rotation speed is maintained.
It shows that the squeal can be produced under vastly different dynamics.
My RS brake squealing has stopped of late on the front, and reduced on the rear. The pads are more than two years old.
The discs won't have altered/worn in a few months to have stopped the squeal.
Yes, likely not a lot, but the thing you've neglected to consider is how the pistons retract (big one) and as well heating and cooling soaks. Many cars (I'd gander say all I've EVER encountered) jacked up after sitting overnight will at minimum drag partially around and most the entire length of the rotation. Whether they squeak or not, well that is a matter of their design and such. Also keep in mind, with vehicle brakes of any kind they ALL "squeak" we used to use special digital recorders to "listen" to this squeak that was above the human hearing range on brakes operating normally. But yes, otherwise we could get them to squeak and chatter anyway a number of ways... I'm totally guessing as well, but the size and such with lower density parts (aluminum calipers rather than cast iron, or HUGE aluminum or more exotic metal) calipers could be a factor in having your brake squeal instead of rub on the stand.
I still do not know for sure which it is you are having an issue with, or truly asking; them squeaking all day on a trip, or sitting on a stand side loaded... That would make your query easier. Frankly sounds like your bearings are lose.. (kidding really; don't know how much variance they should have at proper load - ask Duane, I'm not blaming him today...)
It would seem I am the only one to ever put a cold car on a lift and have to man handle the seemingly frozen up perfectly operational disc while remove the wheel, then with making no changes but removing the wheel and recording said disc thickness drive it around the block to have it spin freely. No? Anyone?
And since this just came in below:
I've done that for years on cars, some car brake pads come that way.
Indeed; by the time I "wrapped" in that area, everything I saw pretty well came that way as well as a cheapening them up by putting only one wear sensor on them - so they could only be installed one way, which was a PITA. Also the backing/anti rattle pads were getting skimpier as well (they all used to cover the entire back.)