You don't have to take the dash out to do the blower motor or the fresh air door actuator. They're under the dash on the passenger's side. For the blower motor you do have to take out the glove box/door, but that's easy. Two clips for the straps, hinge snaps off. Just be careful not to use your mini sledge on that hinge, it can easily break. LOL
Heater core, if that needs changing, can be done without removing the dash. It comes out the driver's side underneath, near the gas & brake pedals.
Just guessing, but I'd say your fresh air door actuator is toast, and it's allowing the door to vibrate and that's the cause of both the "banging" and the vibrating noise you're hearing. That actuator is right next to the blower motor. 3-4 screws and one plug.
One option on that actuator is to get it positioned where you want it and then simply unplug it. You won't have any control over fresh air vs recirc, but you will have peace & quiet. Just my .02.
-1999 Plymouth Grand Voyager SE. Factory Emerald Green, with aftermarket rust accents ("What rocker panels?!") 192,000 miles (and counting) with the 3.8L and ORIGINAL 41TE. The Spinach-Van!
-1996 Plymouth Grand Voyager SE, Factory Rosewood paint with ZERO rust, 3.3l, 175,000 miles. The "new" van. It's a baby. The Eggplant-Van!