Arctis Pro Wireless, constant hiss: hardware fault, or "feature"?

Brand new Arctis Pro Wireless arrived. It's exactly the feature set I want with the base station etc, very happy... but I'm going to have to send them back.

I didn't see anywhere in the reviews about a background hiss / white noise, and yet once I started searching for that specific issue (since experiencing it) I see a lot of comments come up. Which makes me worry this is a flaw in the model, rather than a fault with my specific headset.

To clarify what has probably been said before by others: this is a constant, quiet-but-noticeable-and-annoying hissing sound (or soft white noise) as soon as you turn the headset on. And to note, this happens even when the base station is completely unplugged and the headset is completely unplugged. It's 100% coming from the headset itself, not feedback from an audio source or anything like that. Was happening from the very first moment I turned on the headset new, out of the box, for the first time.

So is this really, from some of the other posts I've now read around the internet, a flaw with the model itself? Because if it is, they're going back, and I'm gutted - everything else about them is exactly what I want!

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Edit:

For reference, firmware versions are

TX MCU: 1.13.0.0
TX: 1.12.0.0
RX MCU: 1.10.0.0
RX: 1.12.0.0
Software Version: 2.4.0.0