Horrible Clattering noise while accelerating

First Post here after 18 months of reading

I own an '03 Freelander Td4 serenghetti (90k miles)and have a problem - the vehicle is sitting in an Italian garage while I'm on holiday and am terrified of what they are doing with it so any advice would be great.

The car whilst ticking over is fine but while accelerating gives a horrible clattering noise from underneath. It first occured whilst accelerating out of a motorway service station (hadnt re-fuelled). The noise was so loud that I was expecting to break down but when I got to 70 mph (or coasting speed) the noise stopped and I travelled a further 100km to destination without any problems. However, on travelling around town, unable to get the speed up, it got worse and worse. The mechanic drained the engine after suspecting contaminated fuel but unfortunately after the engine warmed up, the problem came back.

Whilst pushing the accelerator in neutral, the noise kicks in at around 2000 rpm. I also noticed a bit of black soot coming from the exhaust

Any advice here would be great.

Without more info it is too hard to guess what the problem is. Could be the big ends or main bearings have given up and your engine is about to fall to pieces, could be the catalytic converter has failed and internally broken and rattling about (may also cause the black smoke due to partial blocked exhaust), or could simply be a broken exhaust hanger so the pipe is clanking about and the smoke is just coincidental.