95 ford explorer, filter particles coming through vents?

Probably just some debris coming threw from the outside air intake that is under the windshield, where the wipers come threw, Take off screen cover & clean what you can. If the blower motor is easily accessed take it out and clean as much as you can in the vent system.

Also check the area of the dash where the windshield meets the dash in the area of the vents for the defroster. People have a habit of placing receipts, business cards, and especially bank drive up receipts up there. Then easily slide down where they cannot be seen. The paper deteriorates quickly sitting in a hot car and in the sun and bits can easily slide down into the vents.