exhaust backfire and popping sounds

[pradtf]

we have a bit of it - nothing really explosive.
generally it seems to go away after the car is warmed up.

what sorts of things can cause this?
improper air/fuel mixture?
moisture in exhaust?
leak in exhaust?
timing?

our gasoline is good not old and we have new spark plugs installed.

i would appreciate suggestions on where to start investigation.

[mudkicker715]

Start at timing.

[Jurjen]

And then leaky exhaust near manifold or cracked exhaust manifold.
The exhaust manifold bolts like to unscrew themselves, so check those too.

[BenM]

Way too rich a choke can cause it to cook off in the cat. I've done that before.

[philotomy]

My Olds Omega used to do that, turned out to be a bad choke.

[AMCKen]

As was said, could be choke - too rich or lean for the engine temp until it warms up.