While there are reports on the Internet regarding how loud large HDDs (6TB and above) are, and there has been extensive testing on this subject, after using an HGST 6TB drive for a day, I can safely safe that it's not something you should be worried about. You either have to live in a very quiet room or you have a very sensitive ear to notice the sound. I sure as hell didn't even though I sleep next to my PC every day. Even at midnight, all I could hear were the sounds coming from the fridge and the large fan in my room, and when I turned them off and moved my head close to the PC case, all I could hear was the front fan of the case, not the HDD.
Conclusion: Stop worrying about HDD noise and just buy what you need, unless you are in the case I highlighted.