My air bag pump engages at exactly 30mph and shuts down when coming to a stop.

You will need to scan the suspension module for codes to determine which part is not functioning properly. I would double check that the backing plate is not hitting the rotor and also re-torque the wheels. When doing a brake job the hub surface must be cleaned of all rust an dirt in order for the rotor to run true, especially in the rust belt states. . We use carbide scrapers to remove the rust down to the original machined surface instead of using rotary buffers or sanding discs that either polish the rust and leave high spots or remove too much material cutting into the hub surface. If you have aftermarket wheels make sure you have the correct lug bolt design or they can loosen up if torqued to factory spec. Prop shaft seal will not cause noises in less the center diff has run dry.