Rattling sound from within the engine

Hi!
I just did a swap and used a def 200tdi engine which is running fine but at idle there seems to be some kind of soft rattling sound coming from some where below or in the rocker cover. Have no clue what it is. Checked if anything was touching or vibrating but thats not the case. Seems its inside the engine. Any thoughts on this?

Broken valve spring

THanks will check.

Vacuum pump?