Many thanks to the Forum in flagging this problem. I checked my 2016 D4 this morning and sure enough the top hose has a split in it. Rather than chafing it looks more like its been cut by a knife - not all the way through though. I have wrapped some tape around the cut and booked the car in for a repair under warranty. Ive done 126,000ks and I'm pretty sure that I have already had the top hose replaced at around 70k - same problem I suppose but wasn't aware of the Cover causing the problem and LR didn't say anything.

