My 2001 Buick Century and my 2003 Impala (rental) both do this. It has to do with the temp changes as you mentioned.
My 2002 Camry has no issues of this kind.
Ok both me and one of my roomates seem to have this problem, but I think I
> know whats causing it.
> When driving around, or even stopped at a light, occasionally there will be
> a snapping sound that comes from the dash, it doesnt happen at any regular
> intervals, and is completely random. I THINK that its either parts of the
> dash or the magnesium mounting bracket that they have under the dash that is
> flexing from the temperature change, since I'm getting into a hot car at the
> end of the day (this is Arizona, outside temps are in the 100's, inside of
> cars of course get to 150+) and with the AC blowing cold, theres going to be
> a quick change in temperature causing the plastic to flex.... anyone agree
> with that? more importantly, anyone know the exact place where its flexing
> at where a piece of felt or something would absorb the noise instead of
> allowing plastic to rub on plastic?
>
>