Strange sound of the TDI 110 kW engine

[KarelM]

I have driven more than 2000 km and it still worries me strange sound of the TDI engine. Upon slight acceleration from 1500 rpm, a noticeable metallic knocking/tapping from the engine part can be heard, even when the engine is cold and warm. I have had four different cars with this engine, but none have had this sound. I visited my VW dealer, but they haven't commented on it yet. Anyone else with a similar problem?