Air conditioner/ducting question

[lajitasgal]

Hi all - I've been a lurker on the Forum for quite a while but haven't yet posted anything so I guess I still qualify as a Newbie. We have a 2019 3121 RL, and really like it - bought it new in June 2019. This is the first rig we've had that has a ducted air conditioning system with 2 rooftop units. It cools just fine, but lately I have noticed that there is a lot of black particulate material appearing on the surfaces in our unit, in all areas of the rig. It almost looks like black dust or dried out mold. I wipe it off, but it reappears over the next few days. We live in S. Texas so we do run the air conditioners sometimes when the temperatures get up there. My questions: Do we need to have the ductwork cleaned, similar to what one might do with central air in a home? Or do the rooftop units need to be cleaned? Has anyone else experienced this phenomenon? I never saw this in our past trailers, which were not ducted. Thanks!