There is a thread on this that I started some time back called "bump on start" I think. Seems to be only on the 3 litre motor. I have had engine mounts replaced and a new dual mass flywheel to no good effect. Fiat then sent out a service manual instructing that a new engine mount had been produced that was stronger. Had that fitted - worse than ever. I have been away on a long trip, now back, and I am on the verge of going back once again to the dealership to have it followed up further. Found that levering the motor against the torsion bar stopped it so it is a positional thing I think. Anyway, onwards and hopefully upwards....
Let me know if you have any joy working it out.
Ian.