hello.
i drive a 2006 c200 CDI with auto. transmission.
for the last 5-6 months i have a wierd ratlling noise that appears only in 2500 rpm and higher. it sounds like a very fast "trtrtrtrtrtr" - like a fast drumming on aluminium can. the engine itself is perfect so i guess it has something to do with the components around it. i have checked the electronic manifold that opens and closes and it is not the problem. i ran it for a short time without the belt (alternator, air con.) and it seems that the noise dessapeared but i'm not sure still where it's coming from. my father is a mercedes mechanic and even he's not positive about the noise source.

did anyone see this kind of malfunction before? is it possible that the air con compressor is responsable for the noise? and what is the reason it's only heard in about 2500 rpm?

at first i was suspecting the injectors, but i'm not sure anymore.

will appreciate any help! tnx