Hi Steve,
Wow, that was a fast answer! Off the top of my head I'd say you started typing it as soon as I posted my question :D
Thanks for the feedback. It's interesting that your gauge fluctuates too. It's my first Audi, having owned Skoda, VW and Ford before and all their gauges were rock solid. When I DID have a fluctuating gauge it was actually the thermostat.
I'll keep it under observation, the car still has about 6 months and 15.000km warranty, so I could have it replaced for free probably if it's gone.
Cheers,
Adrian