Wow that's a pretty damn good explanation for it. If it is a software update then it seems like it would be pretty easy for MS to diagnose and fix.
Maybe, but I'm not sure that MS is even diagnosing the software, apparently the problem was there at the US launch too, and MS seem to think it's a hardware going by the official responses on the boards, which means that the following thing will happen...
1. Customer: Wisper silent console, awesome!
2. Customer: System updated, hmm what's this strange noise coming from the console?
3. Customer: - Hey MS my Xbox sounds strange...
4. MS: - Sorry, send it in for repair...
5. Refurbing plant: Yup, strange sound found
6. Refurbishing plant: Testing, ok, factory software reinstalled, ok
7. Refurbing plant: Nice, no strange sound found. Refurbished. Sent to customer.
8. Customer: Cool, my Xbox arrived!
...repeat from 1
At least that's what I got out of the huge threads on the official board about this. So right now it seems easy enough to just make it use a bit more power when idle, if that makes the noise go away.