There is not much that can be done, 3.5 inch hard drives make a lot more noise, as e.g. 2.5 inch hard drives, that would be an option, to swap those 6TB drives and replace them with Seagate Barracuda 5TB 2.5 inch ones, although you would lose 1 TB in a RAID1 config by doing this. As an alternative I cold also imagne that it may be an option to return the Home Duo and buy a Synology NAS DS418 or 420+ and install 2.5 inch Seagate Barracuda 5TB drives (the Synology have 4 bays, so you could populate it with 3 x 5TB seagate drives and have a 10GB RAID5 instead of 6TB RAID1 that is whisper quiet).