Viscuous hub bearing? ( is that the servo pulley below the water pump ? I've checked that and it also seems ok ).
Belt tensioner seems fine ( I did the screwdriver extra pressure and the noise is still there so I don't think the penny will help ... I think the noise is defo the pump ).
An update ...
A couple of days and all seems well. It's starting fine and runnning well ( apart from singing noise ). I keep checking the expansion tank and each time I undo the cap there's a slight hiss but still no explosion so I'm hoping that's saying there's no great pressure building up in there.
Temp gauge is staying solid at about a 1/3rd and the heaters are blowing nice and hot.
The water level is still holding it's own with no noticable water loss but I've only been driving locally.