What does the (AAV) Ambient Air Valve do?

[Mattcamp]

So a lot of people on this board have dealt with the old kazzo in the engine compartment before and have replaced the Ambient Air Valve to remedy but I was curious as to just what this thing does and why do our cars need it? Why does it only make the noise when it is cold outside?

Anyone know for sure out there?

[E Sully]

[Mattcamp]

Thanks Ed.

I think that just about covers it.