engine rattle

I recently sold my high milage 2007 jag estate 2.0 x type and bought a very low milage 2003 c220cdi which still looks like new. My question is although my Mercedes drives lovely the Engine seems to be so much noisier than my jaguar (from outside only) especially in closed surroundings and...

found a loud ratttle in a unit at the top front of the engine, looks part of the cooling system connected to the radiator top hose. what is this unit? is this likely to be a costly repair? assume water pump behind centre pulley... any help appreciated, trying to save my te from the scrap...

my e230 est 1997 is pinking under load, engine top rattle heard. also engine speed hunts wildly at start up, between 0 - 1000 rpm indicated, but settles down after a few minutes. local garage found ecu readings all at zero. recommended replace ecu but unsure it would be the final solution...