THis is what I hear when my car sits for more than 24 hours...I recently was out of town for 3 days, missed the car more than my dog (it was close).
Anyway, I started the car and let it warm up for about 60 seconds, and then slowly pulled away and it went "THA-THUMP" almost like the differential had crusted over while it sat. I noticed it did this a few weeks ago when I didn't drive it for two days over a weekend, and it was sitting in the garage at home.

Both times it was exposed to 40-50 degree weather. Anyway want to guess what's up with this?

 

Assuming this isn't the ABS check, I'd say it's your parking brake.

Mine has stuck after parked for a couple of days, even when the temps have been above freezing. Next time, try leaving it in gear without the brake and see if it happens again.

Disregard the above if you don't use the parking brake.

 

I'd say parking brake too. I get it once in a while after letting the car sit. Now I try not to pull up too far on the handle so the brakes won't grab so hard.

 

My guess is the ABS. I hear it all the time first thing in the morning as the car begins to move.

 

If you put the car away with the brake pads wet and then engaged the parking brake the pads may have rusted to the rotors and the noise you hear is the rusted-on pads breaking loose. It happens.

 

That happens to me quite frequently, since I don't like to drive my car right after I wash it. I usually let it dry at least 3-4 hours before I take it for a spin. The rotors make about the same noise described when the rust breaks free.

 

If it only does it once when you first start out it is the ABS system going thru a self test.

 

I only drive the 8 on the weekends, on the cold days, for the first few miles, I have the same problem you describe.
The tires have flat spotted from sitting so long. After a few miles they seem to warm up and round out. It's weird, I have never noticed this on any other car I've owned.

There you have it!

 

Thanks for all the info. I'll go with the rusted pads/parking brake to the rotors theory. I pull up the parking brake with a nice jerk to make sure it's engaged. I see rust on the discs sometimes, too, and its always humid here in St. Louis. Just another quirk of this lovely machine.

 

Yes, I also strongly support the rusting theory. Happens to me all the time after I park the car when it's wet. It never happens when I park the car when it's dry, so for me that rules out the ABS self-test as a potential cause.