Noise

I have 2008 bmw 335xi sedan with 140 000kms. When the car is cold and i
accelerate (even slightly), i hear a metal to metal ticking sound, as if i were
hitting on a metal rod with a stick. it also apears when engine is warm, but it
often goes away after a couple of minutes driving.
It is not the wastegate rattle, it is not the valves that a are ticking. it is
something else