Anyone else have this issue? Whenever I hit a manhole cover or bump I get a thunk/creak (hard to describe)coming from the area of the driver's B pillar, seatbelt/pillar/door area. Driving me crazy. I peeled back the weatherstrip
and put some butyl tape where the plastic side is a little loose but that didn't fix it. The bezel around the seat belt creaks when I move it around but I don't think the noise is comig from there. Thanks!

 

I have 2006 C4S cab and have the same noise. While car was still under warranty I had the dealer service try to fix issue at least six times. Now at 89,000 miles and I live with the darn sound.

 

Try: Applying silicone to seat rails / changing position of seat / tensioning seat belt

 

I fixed the noise problem although I don't know which thing I did fixed the problem.
First thing I did was remove everything from glove box, center console and door pockets and test drive.
I have read the sunroof can rattle although mine doesn't.
The pillar seat belt adjusters can make noise. Try moving it up as far as it will go then then drive the car.
I took the seatbelt adjuster cover and bolt off and lined every gap including the loose push button with stickyback moleskin which is a thin felt you can get from AutomotiveSpecialties.com. Lined the assembly runner rails as well. No more noise from that area.
Seats/mounts can make noise if no one is in them from engine vibration.

The seat belt surround at the top of the side panel can creak. Removed it and covered all contact points with Scotch Squeak Reduction tape. Note here that to remove the surround the interior side panel should be off the car first. It's a lot easier because the end of the seat belt surround goes into the side panel at the front of the rear window and it's tricky.
The door can thump over potholes if it is out of adjustment or weatherstrip has shrunken allowing it to move. I wrapped a piece of electrical tape around the door striker and the thump stopped. Maybe the door needs to be moved in more or weather strip replaced?
The instrument cluster can and probably will creak. There are posts on how to fix this (read TSB on this) with thicker sticky back felt from a craft or fabric store but if you do, cover the surrounding plastics with a non-agressive tape before you remove anything for protection. The Porsche 'soft look' plastic coating scratches *very* easily, don't ask how I know.
The back seat latch stop bolt can make noise due to the side panel rubbing against the bottom of the plastic stop assembly. I covered the bottom of the plastic stop with Squeak Reduction tape I bought online from Amazon. The 6 mm bolt holding the stop in place rounds out very easily, be careful. The bolt is $19 + ship from Suncoast if you mess up.
If you use a plastic pry tool anywhere put tape down on/at the working area first so as not to scratch.

I removed the side panel, kind of tricky, need to follow the manual for instructions.
I used the Squeak reduction tape and felt tape in any place where I saw friction/vibration possiblities.

I removed the B pillar cover and put SR tape at all contact points. And I put SR tape on the edges of the top pop-off piece (the coat hanger). Potential for squeaks.

I also applied Einzett GummiPlfege (sp?) Rubber dressing on the inside and outside of the door weatherstrip and surrounding strip on the body opening, had to use fingers and Griots foam sticks to spread it under the rubber curl on the weatherstrip. Don't know if this helped alleviate any noise but it sure makes the rubber look like new. Could this have stopped the thunking of the door?

I don't know which fix did the trick but the car makes no creaks or thumps any more.
Didn't adjust the door at all.

All I hear is that great Gundo hack exhaust!

Good luck, hope you find the noise.

 

Dawgdoc-

Sorry I overlooked the fact that you have a Cab, but maybe some of this info may help.