It has always been my understanding that it is the pads which make the noise, not the rotors. The pads are supposed to "slide" against the rotors, so that in itself can set-up many scenarios for various vibration patterns (and sounds). As the friction of the pads might also build a resonance in the rotor, too. Metallurgy MIGHT play a part in this, too. NOTHING is as generic as it might seem!
In prior times, vehicle speeds were not nearly as diverse as they can now be, for the same vehicle and different owner uses. Used to be that most people obeyed the posted speed limits, so a main performance criteria was "under 75mph", rather than over it (as it now seems to be). Figure in generally heavier vehicles too! Then the desire to decrease weight in ALL vehicle areas, including brake pads, so LOTS of parameters for a "good" brake pad. Not nearly like it was in the middle 1970s, when cars seldom got past 5000lbs and almost never exceeded 90mph, or got close to it.
In the later 1990s, a lady brought in her year-old Corvette with the complaint "brakes squealing". An office manager type who drove her Corvette like a Chevette. Yep, brakes designed to reliably stop a car from 175mph being used to "stop easy" all of the time. So I got a new set of pads and the tech installed them. Factory warranty paid for all of it.
Pads designed for "HD" use, even HD2500 pickup trucks, need to be harder yet still have a more aggressive friction material. "Car" pads need something softer and generally quieter, by observation. Fine line on this last item, it seems, as that "one panic stop" capability is needed, too.
REGARDLESS of the vehicle, NO panic stops need to happen until the friction is mostly bedded-in after installation. Yep, "break-in" time and miles/stops. People who immediately go out and "panic stop" new linings WILL have issues with those brakes after that, by observation. We had a "quality control" guy in our service dept that did that. Brakes pulled one side or the other, after that. He basically ruined the work of our brake techs with his "worse case scenario" actions immediately.
SO, all rotors need to have the final "swirl polish finish" the OEM rotors had on them when new. That additional finish operation breaks-up the "phonoraphy needle"-like grooves from the lathe's cutting bit. Otherwise the friction will desire to follow those grooves inward until the pad has smoothed them out. Chattering and such can happen with no swirl polish. IF the finish is too satiny, early brake fade (and smells) will happen until that finish is polished by the pads, too.
Which is ONE reason to not cut a rotor when brake pulsations in stopping. The new finish could be worse than the current one, even if there are some wear grooves in it! New pads, easier stops initially, then it can be longer until the next need for pads, from my experiences.
MANY seem to desire "drilled and slotted" rotors for alleged better performance (which they can provide in some racing and mountain-driving situations), but definitely overkill for normal uses, to me. PLUS, no machining of them as you would for a normal non-drilled/slotted rotor. Just replacement.
About 6 years ago, we bought a full set of brake parts for a British high-end, but smaller model thereof, SUV. Rotors, pads, wear sensors, seals. Our dealership cost from the OEM dealer was $1400.00. Then figure in the labor price at whatever is prevalent in your area for such. No wonder they were on our used car lot!
Same surface finish things also apply to drum brakes, too.
Just my experiences and observations,
CBODY67
