Ford Focus 1.8 tdci sport. Clunks when i come off or on the throttle?

Hi, i have just bought a ford focus 1.8tdci 2010plate, the car has been back to Arnold Clarke 3 times in 4 weeks for fault. First a fuel leak and brakes knocking, 2nd time the drive belt pulley and idler were squeaking and needed replacing. Last time was for a clunking noise when i come off or on the accelerator pedal. I thought it was the drive shafts or gearbox. They told me they had sorted it but when myself and the manager took it for a drive the clunking was still there. The manager said it was coming from the gearbox. He then told me that this was normal for the 1.8 diesel engine to do this. This noise is not quiet and i have never heard it before on any other car i have ever been in. Everyone who has been in my car has commented on the noise as being unusual. The manager said that if he replaced the gearbox the noise would still happen. I'm not convinced. Does any body have any suggestions or has anybody experienced this before.

I've noticed noises like this before coming from the cv axles, cv joints, broken or loose motor or transmission mounts.Loose, broken, or worn upper strut mount and worn ball joints also causes similar noises.

I had it with an XR3i. It was just transmission slack although at the time I suspected a worn gearbox mounting. A Ford mechanic road tested the car and instead of ripping me off said it was transmission slack which was common in this car. Your diesel has a lot of torque so I expect that contributes to the effect. You could always ask a Ford garage for an opinion.

The manager said it is in the trans and then he tells you it is normal and if he replaces the trans it won't cure the noise. And that is after they claimed to have fixed it. It looks to me that Arnold Clarke's is not the place to take your car.