So are you saying they all have this fault or are you just relunctant to return it for some reason ?
It sounds like a ground loop.
I don’t fully understand the why and how, but maybe @amirm or @Buckeye Amps can explain (because there is a YT video of someone with the buzz with Buckeye Amps and the Node Icon).
I have had this problem with a Yamaha Cx-A5100 which is a two prong AC power product with XLR out. The problem is that the XLR pin 1 needs to be chassis ground (not signal ground) but the chassis itself is double insulated, so there is no ground. In theory, the floating ground has to come from the downstream product (I think).
With my Meyer Sound gear, it is a three prong AC power with the XLR ground going through a resistor to the earth ground of the AC.
When you connect the two prong Yamaha to the three prong Meyer Sound speakers, you will get a ground loop.
I actually saw this problem when measuring my Marantz PM-10 which uses bridged HypeX amps for a balanced amplifier (with no ground, the black speaker terminal is negative voltage) and also is a two prong AC power.
The fix for the hum involves grounding the 2 prong device. For the Yamaha and Marantz, they have a phono ground lug which I can connect to the earth ground of my surge protector. Using a Panamax line conditioner, there is a simple ground lug screw to use for this purpose, but internally it just connects to earth ground.
Something like this should work too, if I didn’t have a Panamax product.
Static Care ESD Grounding Cable... https://www.amazon.com/dp/B08V5D9L7L?ref=ppx_pop_mob_ap_share
The problem now arises with the Node Icon. Two prong power, so it’s ungrounded, just double insulated. If you are using eARC, the TV is typically also two prong power, ungrounded.
My assumption is that the shell of the RCA out is ground, so if you tied that the earth ground that matches your amplifier, it would eliminate the ground loop at idle.
Now, the confusing part is that there is signal ground, chassis ground, and earth ground, and they are different but can also be tied to the same ground…. Likewise, I am not fully sure why the presence of a signal removes the hum from the YT video (most ground loops are always there). I am not sure if the music masks it or if there is something that happens when there is a signal.
Based upon the YT video, if the buzz goes away when music plays, I would reach out to Bluesound again and suggest the following software fix.
There needs to be away to output a 1 bit sinewave at 48 kHz, which should be inaudible due to both amplitude and frequency at idle. They need to program the 12v trigger to not consider this as a signal and to still power off the downstream 12v trigger if there is no content actually being played. This should keep the XLR outputs in an active state which might address the ground loop.
Alternatively, they need to make some sort of dongle that allows you to ground the Node Icon. Maybe a pass through device where you still can use the RCA outputs (or inputs) but have a wire to ground to avoid the DIY nature.
This is the YT video
I put my order for the Node Icon through TMRAudio last weekend, and they expect their next shipment to go out later this month.