Wow thank you so much. that appears to have been the problem

My pleasure.
By the way I would still not generally recommend setting the fan above 80% due to the design flaw that makes the higher pressure 38mm fans blow so hard that the low pressure fan 25mm is spinning but air is moving backwards through it.
Does that apply on the batch #3 too ? Not had the case off mine but it appears from the outside to only have those 2 high pressure fans, changed it anyway.