Update. I never did find out where the noise was coming from. For the past several years, I changed out all 4 rotors and brake pads as needed. The only thing I noticed was the brake pad on the front passenger side had some uneven wear and sometimes the caliper would spring back a little when pressing them in. I had cleaned the caliper pins and lubed them accordingly the entire time, but still the same result. They weren’t damaged or rusted. I ended up selling the van at 250k miles. At that the point, the noise was reduced, but still there.