Cliff, my 2005 XG350L does the same thing every once in a while cant figure
it out...With the temps out here ( gonna be 112* today ) I dont think
moisture has time to form...Hmmm come to think of it I dont ever remember
any liquid under the car after shutting it off.  Here in Las Vegas my air
runs from the beginning of March till around the end of October.. EVERYDAY !
I have never talked to the dealer about it because it only lasts for a few
seconds and is gone and is more like 110* stinky air.

The problem with AC is it always generates moisture. Even if you don't
see water dripping it is there. Unless the cabin fan runs for quite
awhile after the AC and motor is stopped that moisture is just asking
for mold and other stinky stuff to form. If your car sits outside and
the temps get extreme it may be enough to kill off these mold spores
but they are VERY resilient and that is why you get that stinky smell.

I service my cabin filter regularly which helps a little. You can also
pickup a product called Frigi Fresh which helps. It is the same stuff
the dealer will charge you big bucks to spray into your system. BG
Frigi-Fresh is formulated to quickly and effectively remove foul,
musty odors from automobile air conditioning systems. It kills mold,
mildew and other odor-producing organisms that grow in the evaporator
core and housing and costs about $10 a cab. I think the cabin air
filter is installed before the evaporator so if you dont want most of
what you spray to end up in the filter media I recommend servicing the
filter and just before installing the new element spraying the
Frigi-Fresh into the housing at the same point as the filter so it
permeates the evaporator core. That may provide the best and most long
lasting results.

Another tip is to kill the AC blocks before garaging the car. That
will "dry out" the evaporator housing and limit the moisture that
stays in the case.

Old cars using R12 had less problems than new cars using R134 as they
ran colder liessening mold growth.

Good luck.

My dealer did it for free the first time. Thereafter they wanted $50
to do it. I deferred and bought a can and did it myself.