Are you 100% sure about that? I don't see a C63 in your lineup...just sayin'.

Rattle free 2011 here with 9000 miles

But my drivers seat doesn't sit tight in the track (best way to describe it), it will lift the seat just a smidge under very heavy braking or sometimes when I plop into the seat (because I can't rub the bolsters)--it's been this way since delivery and I mentioned it to my tech last time my car was in for fluids--he said they do about one of these repairs a week The kicker is, the whole assembly needs replacement and it takes 8 hours--I was hoping it was just a loose bolt, but he said no way, it's a defective part from an outside supplier--I've learned to live with it, but it will get done before I'm out of warranty or buy something else!

OP, sorry to hear about your troubles, no car over $50k should have rattles IMO, a six figure car is unacceptable--C class or not! GL, hopefully you can get it rectified.

My 2012 BS has the rear shelf/brake light rattle. Also the rear side panel where the speaker grill is and there is a bad vibration from the subwoofer. It's going in on Wednesday to get fixed.

Is it a common problem in all c63 coupe or BS?

I agree, i hate cars that rattle. thats when i know its time to replace it. I don't think the C63 was designed from the ground up to Handel such heavy forces. We have basically a reinforced C class frame and body with stiffer suspension and short sidewalls.
Nevertheless, It's put together well which is why some people are reporting no rattles. Most stiffly sprung cars will eventually rattle and loosen up. I wonder how a Ferrari, driven as a DD hard over potholes etc, would hold up after 30k miles.
All my sports cars eventually have started to rattle. Corvette, GTR, M5, gallardo.
My E500 and BMW 550i were softer and had little to no ratels. So was the Toyota camery I rented with 30k miles on it. Our cars Have so many parts and pieces attached and screwed together, so much can go wrong.

I am not sure how my dealer fixed this. I think they ordered a new unit and replaced the offending piece.

I think only the BS has the rear parcel shelf if we delete the rear seats. So I don't imagine this issue affects other C63's. My dealer said something about the 2012 parcel shelf not being designed correctly and that a new one being ordered would address the rattle.

My pano roof has squeeked since day one in my C BS, my interior panels squeeked from day one in my CLK BS, I just learned to deal with....and long tube headers and cat delete help a ton.

GTR rattled lots, and so did 2008 W211 E63 that I just drove this past week with 19" wheels -LOTS of rattles all over the car, perhaps the Panoramic roof?
I also test drove a E63 wagon and it rattled quite a bit. Bottom line, these MB cars are not equally well made and I think it takes a bit of luck to get a solid one.
The GTR - the all rattle, but the drivers don't care!
PL

Actually, it does have a very rigid chassis. Car and Driver called it G-wagon vault like. That's precisely why the interior rattles are more likely to occur: very stiff chassis and suspension means the forces are being absorbed by the interior trim bits. Think about it- a soft, flexible chassis would naturally absorb more road imperfections.

I have about 1500 miles and only a VERY minor rattle from the rear. Think it's the parcel shelf.
Also driver's seat side bolster would sometimes squeek when shifting body side to side, but that seems to have gone away.