If you do, I am willing to bet that there is original home construction debris (dirt, dust, nails, pieces of wood, etc,.) in that duct from the builder’s subcontractors walking through and getting the house ready for its first occupants.
You may want to remove the registers and vacuum out the debris…
After 30+ years, I have found almost every home that has floor HVAC vents had some sort of debris in them…yours will too!