Knocking Noise From Cold Start On Fiesta Zetec 1Lt Ecoboost

Looking for anyone with similar experiences with their Ford Fiesta Zetec 1lt ecoboost,

Upon starting after 30 seconds I experience a knocking noise from engine, once car has warmed up noise goes away, knocking noise is as loud as a cold diesel engining starting and is very noticeable when engine is idling, but goes when engine is rev'd up or driving but comes back when stopped at lights.

Been into dealer twice this week, first time the moved gear linkage cables, and it was gone, drove to shops and when came out it was back, so took it straight back to dealer, who went out on test drive to hear noise again, this ime he got me to pull over at side of road, lifted bonnet, but noise was only audible inside car , till he braced engine with his hands and noise stopped as engine vibration was reduced, and whilst touching air box on left, it stopped totally, all was fine to next day and noise is back, dropped car off last night, and when collected it today, they are trying to fob it off as an engine note noise and a chararistic of that engine, which I know as a croc of sh*t, and got the impression they haven't a clue, so fobbing me off, phoning ford tomorrow, but wanted to check if anyone had has similar probs, oh and engine only done 4900 miles in 22 months, any help or advice appreciated cheers jim