I had the exact same problem with my 2002 CLK430 cabriolet. Everything seemed fine 99% of the time, but when I drove over and uneven surface diagonally--- like pulling into a gas station on a slightly higher grade than the road --- I could hear a distinct THUNK from under the car. Mine sounded like it was coming from the forward part of the car.
The problem was a loose bolt that holds together a couple of pieces of metal that add structural support to the vehicle. I think they are specific to the cab, but not sure. Solution was to disconnect the pieces, clean them off really well and bolt them back together REALLY tight.
If the problem is ignored for too long, the pieces in question can degrade to the point where they must be replaced at substantial expense. This was not the case for me. I think the cost at my local German Indy specialist was less than $100 for the fix. I haven't heard a peep since.
Under the dash by the driver left foot.
Rain tray, driver's side.
There are two levers under the driver's seat of the 1992 Cabriolet. One lever moves the seat back and forth and the other offers a tilt option.
driver's side dash. between the hood release and the clutch pedal
Under the hood in the driver side rain tray near the antennae.
red flag with a diagonal white stripe
The fuse box for the 1996 Audi Cabriolet is under the hood on the driver's side in the area where the windshield wipers are (behind and above the cowl). It's right in the corner of driver's side. Snap open the top cover, slide to the right out of hinges and remove fuse cover.
The turn signal flasher on the 1987 Volkswagen Cabriolet 1.8 liter FI SOHC 4-cylinder is mounted in the fuse panel. Look under the dashboard on the driver's side.
On a 1986 Cabriolet, the fuse panel is located on the firewall in front of the driver's left knee under the dash. The 1986 and 1985 are almost identical in all respects, so that is where it should be on a 1985.
It is located on the driver's side on the firewall next to the Break vacuum pot or cylinder. This description fits the 1999 and 2000 models and i am not sure about other models.
If you are looking for an Audi Cabriolet, here are a few auto dealers you might try: Audi USA, Atlanta Audi Dealers, Audi North America. You may also try 'traders' such as Car And Driver, Auto Trader, or Motor Trend.
day cab is a truck with no sleeper, just a standard cab