OK.. former VW/Audi tech here. I'm having the same issue and have read over pretty much every related thread.
1. I'm absolutely sure it's not the sensors, there's multiple people running them zip tied away from the caliper and still having the issue so that eliminates them as the culprit.
2. For anyone claiming new pads have fixed their problem it's far more likely that having the braking system apart and back together has temporarily quieted the noise, but not solved the issue. This is illustrated with the many posts of "it was gone after new pads, but returned a couple months later."
3. Op's dust shield contact theory is decent however the noise is clearly rotational and varies with wheel speed. The contact point he speaks of is static without rotational effect and could cause a squeak, but would also be easily verified by simply pushing the car up and down.
4. This leaves the e-brake pads.. Many have stated that the problem is directly correlated to parking brake usage and I can attest to only having the problem after using my parking brake for the 1st time (auto). It seems obvious that the brake shoes of the parking break are ever so slightly dragging after the car gets hot (rotor expands from usage, but the inner hub were the parking brake shoes contact would actually decrease in size).
So the question I have is this: Has anyone tried simply adjusting the star wheel to pull the shoes away from the hub? OP stated his method has fixed the problem, but in addition to lubing the contact point he adjusted the parking brake star wheel. My money is on the star wheel adjustment as the solution, which would also explain why people have "fixed" the problem by having the dealership replace the entire braking system. In order to replace the rotors you would have to readjust the parking break and I'm 99% sure that is actually the wild goose everyone has been chasing.