I have the same problem, but you can stop it by selecting the air recirculation button. Had the same on a 405 as well. No idea what causes it.
It's located behing the glove box I found mine by turning on the flashers and following the clicking sound. You will need to pull out the glove box to get to it.
the fuse box is in the glove box, u will see it as you open the glove box it is on the top and drops down
Under the dash behing the glove box.
The BCM (Body Control Module) of the Passlock system is malfunctioning. It will need to be replaced. I just had it done to my '03 Impala.
fuse 14 in glove box
To the left of the OPEN glove box
On the passenger side, to the left of the glove box
Its inside the glove compartment on the left....
I might be behind the glove box.
in the glove box on the left hand side
its your blower motor
If this clicking only happens when your turn indicator or hazard lights is on it's the flasher unit working. If not it's the stuff in the glove box rolling around probably.