Thanks for the added information! Is this an A4 or M6 (since the brake peddles are different)
I would first check where the brake peddle connecting rod goes through the firewall. Maybe some trim has come loose and is binding on the side of the connecting rod to cause a squeak when the peddle is moved. Otherwise, I would lightly silicone spray everything on the interior of the brake assembly (especially all of the mechanical connecting points). If that doesn't work, that's all I have without a schematic for ideas.