Saturn HVAC vent noise

saturn
noises
sc

#1

I have a thumping sound comming from the vent when the blower is on med/high or high. The sound is only presentwhen the directional controls are on full frontal, defrost/floor and defrost full. Is this a duct problem or a baffel/diverter problem? Do I have to dissassemble the entire car to get to the noise?