Hi hope someone can help me, i have a 52 golf gt tdi 150, over the last couple of days i have noticed a strange noise on start up from cold, the noise continues upto around 1500 rpm. it seems to clear once the engine is warm which takes ages, the noise is like a tapping / knocking and as if its only fireing on 3 cylinders there is also a suction noise, could this be caused by a faulty glow plug, there are no warning lights on, cheers