I have recently (4 weeks ago) purchased a 03 plate Mercedes C220 CDI coupe. On picking up the car (which I did test drive but didnt notice at the time) there are several things which I'm unhappy about. The seats squeak at the tiniest movement and the drivers seat is incredibly uncomfortable on long journeys.

I recently drove a 2 hour journey home and I had to stop several times to stretch my lower back as there is just no lumbar support. I have tried the seat in every possible position but it makes no difference. I've driven hundreds of different cars in my life and I've never come across such an unforgiving driving position as this Mercedes.

Of most concern, however, is this knocking noise coming from the rear of the car when I go over the slightest bump in the road. I've checked the boot and removed everything in the spare tyre well to try and isolate this noise but to no avail. I then took it back to the garage who replaced some of the exhaust mountings but this had made no difference.

I'm very disappointed with the vehicle and would like to know what you would do in this position. How long should I pursue rectification with the dealer before I either reject the vehicle or just put up and shut up?