EDIT: Confirmed, just tore it down and tested, definitely the fan on the SBC causing the issue. Disconnect it and the sound goes away but I'm not too keen on letting it be passively cooled. I've disconnected it temporarily because I need to be in my office and the sound is driving me mad. Keeping an eye on the temps just confirming if it's safe to do so or will I need to keep the device off?
EDIT2: I wasn't comfortable leaving it without the fan so I tried to tear the fan down to get to the bearing but being a totally sealed unit that was a no go. Instead I gave it a bath in some WD40, that has made the fan totally silent now but I'm sure it's only a matter of time until the noise comes back
Yea been searching for years (since the moonlander days) for a reliable 25mm fan manufacturer and have yet to find a quality one. Either these work well or they will go bad fast. Just send us an email and well send out a a few replacements.
Fan is only really needed during the initial node sync, but if your using the system for more stuff other than just mining and running the node should probably leave it on. CPU temps are good up to 85c on this.