Same problem on every MDX. I've been considering asking Acura to address it, but thought about it and realistically, nothing would change. Part of it is the seat belt buckle's thin metal attachment bracket. It wobbles with each bump. It does this on my back seats too, but is more apparent with the seat right next to you while driving. I suppose we could jam something around the metal bracket to stop it from wobbling, but seems rather tacky. I think the other part is just the seat springs in general in the base and backing are vibrating and resonating through the entire seat.
Let me know if you pursue it and get a fix for it. I personally would love to get rid of this as well.
this is part of the flimsy cheap parts now used on this car. My passenger seat does this as well on each and every bump I go over when no one is sitting in the seat. My 2014 MDX now has also developed a creaking sound. Whenever I am at low speeds or coming to a stop, it almost sounds like the mast on a ship. It creaks. I cannot determine where this one is coming from. I thought it was the brake pedal part that goes into the dash board but I am not sure. Acura wanted to take as much weight off this car and the mileage is much improved, but as a consequence we now have other issues.