Lately its been subzero out.
When I start my SSE after about 10 seconds I get a loud BANG out of something
in the heater duct.
It only does this when extremely cold out and if I put the climate control on right away it doesn't do it.
Is there a vacume device that is suppose to hold vacume when the car is off?
Is my heater damper door sticking only when cold?

There are vacuum devices but they return to a "off" position once the engine vacuum disipates. Nothing that is supposed to hold while off.

My theory is the same as yours: a sticking door. Maybe there'* even some moisture on the rubber surround and it'* a little frozen.

Had the same thing happen on our car in Florida. The defrost diverter sero gets out of ajustment and closes the door so far that it wedges in the duct. I was able to reach up iand bend the actuator rod (this one starts above the gas pedal and goes up at about a 45 degree angle) so that it did not close quite so far. No more pop.

Thas exactly where the pop comes from.
It sound like someone is shooting a gun at you. Will wake you up in the morning!
How much did you bend it Padgett?

Don't really remember, it was several years ago. Is just a niggle at the back of my mind that there was an adjustment and did not need to bend but am just not sure. Can say it has not popped since.

so if theres an adjustment I'll just make it a liitle shorter and see what happens.
Thx