If you are just starting to notice the dust and insulation in the home I would definately rule out a duct leak.
Since the unit is new there is a possiblity that a leak developed during installation or right after, especially if there is no history of the problem.
If you can rule that out then you are at the managing phase of the problem until you change out the disintegrating duct work.
One way I learned to check for leaks (from an old tradesman) was using the door trick
. Basically close all the doors and windows and try to determine if there is airflow in or out of the home.
In your case the odds favor a return leak due to the excess insulation being blown out. See if the fibers match what is in the attic (fiberglass, cellulose etc).
Good luck to you