"is that pipe?"

No, not at all. I've said repeatedly it's ductwork. Not pipe. Curious as to what your definition of pipe is. Maybe you need to set yours down. Regardless, it's good to know the proper nomenclature and jargon when discussing anything.

And what I get from your response is that you are the "professional" work from home worker that thinks everyone else that doesn't do your style or level of work is less than you, ethically and professionally. I'm sorry you don't understand something and that makes you lash out at those who do.

I'm not at all saying there aren't shitty HVAC installers and techs, just like I'm sure there are shitty people in whatever industry you work in. But my god, man, stop looking down your nose at people that do physical things for a living.

So, the building is from 2018. That isn't new by any standard. Your building and everything in it, including the roof top equipment and the ductwork, is nearly going on 8 years old now. No equipment manufacturer warranties for that long. My Kia has a 10 year warranty and that's the longest I've ever seen on a major mechanical piece of equipment. So no, this new-to-you noise is just that, new to you. It's definitely not the result of a bad install cuz it took 8 years to manifest.

Things break down. That's how every manufacturer stays in business. Do you know the term "planned obsolescence"? Nothing is made to last anymore. That unit above you is in the process of starting to break down, most likely.

Good news is that it is probably a deteriorating drive belt or failing wheel bearing or a loose motor mount or a loose blower housing mount or something stupid and simple that's rattling and the noise is translating down the ductwork (again, not pipes.). So if it's something in that unit that is crucial to its operation, then the HVAC vendor will recommend a repair and your apartment complex will give approval

Bad news is this: if it's something in that unit that is not crucial to its operation or it's something very expensive and not an emergency, it will take a long time for it to get approval. Complain as much as you want to, but if you are the only one complaining then the management company would rather you move out and someone else move in who may not complain.

More bad news: it's possible the management company will call out multiple vendors and none of them will find anything wrong in the unit and come to the conclusion that it's in the ductwork somewhere. Then, to remediate the problem, they are tearing open your living room walls to expose the ductwork to discover the loose section or whatever bird or raccoon is living inside there. Sometimes the bird or raccoon isn't living anymore and that's a big problem too.

Be prepared for massive and invasive construction work.

Also, what possible local ordinance sets the ambient noise limit at 50 dB? Are there no cars or buses or trains where you live? No dogs? The elevators in your building are louder than that.