tappet noise merc e280 cdi

Hi all, i am from India, i just bought a Mercedes e 280 cdi, 66k kms run. I am facing some noise problem inside the car in idle position and also in running. I m really bugged up by this noise. After opening the engine cover, i found the noise coming from exactly top of engine on the right side. this is some kind of tappet noise or injector. however the car's acceleration and running is extremely fine.

Please help me in this regard. thanks and regards.

Zaid
India.