My C36 is not my daily and weather in Midwest has just started warming up, but when I start car after sitting for awhile a clunk noise from around passenger floor board can be heard after a few seconds after car is running (almost sounds like I'm locking doors). Any thoughts?

A noisy relay perhaps?

I wouldn't even know how to diagnose that unfortunately. It has stopped completely whatever it is/was since it's not freezing here in Midwest anymore though and driving it more often.

does it clunk just when you put it in D-mode?
maybe your trans mount is shot?

I had a random clunk when taking off, it was the tranny mount.
had it replaced never heard that clunk again.

you also have two chicken leg plastic stabilizer rods in the rear axle.
one rod on each side.
see if any of these arms has worn rubber bushings or plastic arm is snapped?

Actually it would make the noise after the engine is running for a few seconds (a delay in noise) before putting it in gear which is always reverse to pull out of garage.

is it from the vent system?

It could of been mickey what are you thinking? Again now that it's warm it doesn't do it which is good in a sense, but of course not because I can't repeat for now.

I think its called duovalue for climate control. makes a loud clunk noise over by the passenger side behind the dash when they stick (turn on/off climate system). i think you can clean it up, not sure but i should do something about mine. DR. B might have done a write up on it.

pretty sure mine does it on startup too if climate system is on

Yeah not it, but appreciate the ideas guys. Guess I'll have to wait for cold weather again to try and pinpoint noise spot better.