What's your opinion on out-of-spec. runout on a newly installed rotor? Do you think that could cause a brake to develop pulsations prematurely that feels like "warpage"?
A couple of variables may be at play here. For example, it could be the result of uneven mounting due to crud/rust on the face of the hub or inside the rotor. Could also be a few overly-tight lugnuts.
The most common reason is said to be uneven brake pad material deposits across the face of the rotor. Envision driving down the freeway at 70 mph and making an exit with a stop light at the bottom of said exit. While slowing from 70-to-0, the brakes get extremely hot (as they should). While waiting for the green light, you keep your foot on the brake. This brake pressure, although light, can "cook" pad material onto the rotor at the contact point, creating something of a high point. Pulsation therefore can be the result of several areas of deposits on the face of the rotor(s). This is why simple "clean-up" cuts/rotor resurfacing is effective in most cases. Another reason could be the lack of maintenance on caliper slide pins. Any degree of crud or rust can easily seize guide pins, which may result in calipers becoming slightly cocked. Left for a long while, the pads will wear quite unevenly.
I've been studying this phenomenon for many years, as the idea of warped cast iron has always been ludicrous to me. We're talking about cast iron, not a Home Depot 2x4. While iron can in fact deform at very high temps, this deformation is temporary. Warpage would be a permanent condition, not possible at the temps experienced by passenger cars. Over the years I've developed many habits insofar as brake installation, maintenance, and usage, and have never again experienced pulsation. These include:
1. Make 100% sure hub faces are clean and free of any buildup before mounting rotors. A drill-mounted wire brush works well.
2. Torque wheel lugnuts to spec -- every time.
3. Always bed new pads in accordance with manufacturer instructions. This is very often neglected. Propper bedding will effectively "marry" new pads to the rotors and will greatly aid in resisiting unwanted material deposits. Bedding generally involves a series of very hard and fast stops without actually coming to a full stop (going from 45-to-5 mph, for example). Doing this correctly will actually melt a nice & even coat of new deposits across the face of the rotors. This is also very important for the extremely prevalent ceramic pads we see these days. It can actually be something of a smoke show as the new pads are super-heated and cooled, but that's how bedding works.
4. Understand caliper slide pins are maintenance items. At least once a year, pull each pin, clean it, re-lube it with high-temp brake grease, and re-torque it. This process literally takes less than a minute per pin and will ensure the calipers slide smoothly. This is, of course, only for sliding calipers. And if the rubber boots are cracked/worn, replace them. Very inexpensive.
5. Pop your trans into neutral (or even park) at long stops if you have an automatic and it's safe to do so. Just like with a stick-shift, you can safely sit on flat ground without rolling and keep your foot off the brake pedal. This also prevents hot-spots. This has been a habit of mine for many, many years.
The bottom line is most pulastion is caused by installer/user error. Humans don't like being told we messed something up, so we reflexively revert to the "warpage" myth to cover our mistakes. I fully admit I used to simply pop new rotors and pads onto my cars, drove like a bat out of hell, and never used a torque wrench. Once I understood the science and mechanics at play, brake pulsation became a thing of the past.
There are many good articles out there to further explain. Here are a few:
https://aftermarketintel.com/the-biggest-brake-rotor-myth-debunking-the-warping-fallacy/
https://ricksfreeautorepairadvice.com/what-causes-brake-rotor-warp-debunking-the-myth/
