A170 W168 engine bay noise

[MechNoxer]

So i recently got a A class 170 diesel automatic. And sinds the day i got it there is a noise coming from the engine bay. Its only when driving around 50 but its not constant, It happens to higher speeds but seems random. There doesn't seem a loss of power or nothing feels weird when it happens. It sounds like wind moving somthing but also kinda sounds like metal scraping / grinding. I havent been able to repuduce it when getting up to speed and putting it in neutral and giving it some revs it seems to only happen in drive but am not sure about that.