So, many years have passed, but the noise did not. Today I finally pulled the Nexus out to take a look.
The noise was the ebm-papst cooling fan on the back by the gas hose connection.
Cooling Fan : EBMpapst
After being able to unscrew it from the back of the oven, I ran it when it was not touching the rest of the oven. Still made a bit of a noise, but significantly quieter.
So it appeared to be mainly due to how it was connected causing a large amount of vibration. I noticed that there are no “dampening” materials between the fan component and the metal panels making up the back of the oven. So, I got myself a heat tolerant silicone mat and proceeded to cut some pads and “washers”, that I then used where the various components and panels joined. this was only in a couple of places.
While I suspect replacing the fan for ~£100 may make things quieter still, the difference is significant and I noticed my normal irritation failed to surface. I feel like the oven is now talking to me rather than shouting, and I no longer clench my fist with frustration and disappointment when I turn it on.
I’m looking forward to having friends over and not instantly apologising for the cooker’s behaviour in front of guests.
Perhaps in another 9 years time I’ll actually replace the fan and it’ll become a whisper. I may then even enjoy the ££££ oven the way I had hoped I would when I bought it…. Until then, adiós dear readers