Well it seems like I've sorted this issue, so would like to close it off and document for those who may have a similar problem down the line.
I went through the summer without fixing it as a lack of heating wasn't an issue! Lived with it until Christmas, but then it seemed to get worse. Freezing cold air delivered from dashtop and windscreen vents only tempered by switching to 23 degree manual heat from dash vents.
As the cabin temperature sensor in the centre console is an easy change, I decided to do this first. Not sure it was the problem, but a 2nd hand part from eBay was only £10, so nothing to lose (FoMoCo part 6G9N-19C734-AB used on lots of Volvos, Fords and Land Rovers).
I had a small rattle/buzzing from the bottom of the centre console, so decided to fix this at the same time.
When changing the temp sensor, I noticed the original part had a rattle when shaken, which was not there on the replacement. Could this be my mystery noise?
Anyway, temp sensor changed and reassembled and the rattle has gone. Test of the CC and all is working as expected. CC now set at a sensible self-regulating 20 and very comfortable.
Original fault code also disapeared from VIDA: - CEM-B10EA14 - Positive Temperature Coefficient heater - General Electrical
Fantastic result!! Thanks to all that helped.
