Start though by checking the service of the car, check if it has a clean air filter, a recent (ish) fuel filter change. This would restrict the main ingredients and cause the car to stammer under pressure when it needs the power, and its fairly cheap to replace the fuel filter / much cheaper to replace the air filter!
Otherwise Could be engine mounts are vibrating to be honest, if its only when you floor it, the engines going to work harder.
Hi wounder if anyone can shed any light on this, if accelerating hard from below 2000rpm when I get to1800 theres a werid kind of rattle noise I dont hear it when accelerating normally just when my foots down its a 2.0 tdci focus 07
Does it sound like its a metal on metl sound? I had a simillar issue with mine and what I found was that the heat shield on the turbo was hitting the steel radiator pipe and by pushing it back and putting heat resistant tape on stops the two rattling together,
I would say check heat shields too, but would check all of them as they are prone to coming loose and vibrating off each other and the car,