If its a sweet smell you may have a heater core leak and the fan is blowing antifreeze thru the vents. If its a moldy rotten smell you have mold growing in your vents. This happens when the moisture does not drain properly causing mold. You can purchase a spray at most auto parts store to kill and stop this and refresh your air vent system.
funny as it may sound there might be a dead mouse in there happened to me
Heater core is leaking
A rotten egg odor may indicate a dead rodent or animal in or near the ventilation system, whether in a house or car.
A auto vent
It is common for condensation to accumulate in the evaporator core and cause an odor. There are air freshoners that can be sprayed through the fresh air intake and help sometimes. Contact the ford dealer.
Stopped up vent or improperly installed vent.
You probably have mold in the heater vent ducting.
Transmission overfilled ? so when the transmission fluid is heated up it expands and comes out the vent tube Have you been driving through water ? Got water in transmission so its overfilled , resulting in transmission fluid coming out of vent tube
Check the overflow pipes and pans to be certain that they are not clogged.
no it has a vent if it is coming out the vent it is over full.
Heat is coming from the engine.
check your furnace or kitchen.