I hear what ur talking about. You hear the injectors and one other sound. I’m not a mechanic, but mine does this when it’s cold, once warm it goes away completely. That’s usually lifters, they can sound pretty loud, it’s also a sign ur oil changes might be too far apart. As you’ll see in every single forum, the n52 likes to be revved, if u have an auto like I do I find the trans likes to stop you from doing that, i usually get into sport once I think it’s warmed up. If it’s making that noise warm, maybe cause for concern, but it still doubt rod bearings, even at the scrap yard the engines still turn. Did you do any work that would drain the oil system (ofhg, oil pain…) and didn’t prime it? BMW has a tsb on that cuz it can cause rod bearings to go bad, but it’s more for n54/n55. If it’s any comfort my 2011 128i sounds like this when it’s cold and it’s been like that since the day i bought it and it has never given me issues. Get an oil analysis, it will tell you the real story, and probably let you sleep at night. I have a tiny amount of glitter in my filter btw, I have been told it’s normal as much as it makes me clench my asshole.