Thanks gomezz.
I reset it to “Energy Saver” mode (not called High or low Eco), and then after a short while the normal tv signal failed. By altering back to “Smart” setting the normal tv source now works.
(Incidentally, the settings can only be accessed through the YouView system, and not through the box “Help” link)
However all this does not explain why it is whirring at 10.00 this morning, and just about the whole day?
Also there are no mobile apps set.
I am now wondering if there is a bug in the whole thing and whether if a complete factory reset would be best?