Hello!
Did this issue be sorted out? I've kinda same problems with 1.6 cr 6-speed greenline 2015: at approx 50mph but also at 25mph can easily be heard whining with constant speed and engine/powertrain on light load. When decreasing or accelerating speed rapidly cannot be heard anything.. I've thought it is some kind of resonance or differential or secondary axle bearing... The noise is also almost same kind with every reasonable gear being used (3, 4, 5 at ~50mph) but 6th makes other resonances because of extra low revs tho so cant say properly about it. However, the noise is really whining or whizing, so dmf wouldnt be my first choise (?)
The car is mostly new to me, have driven it about 3k kms. 193k kms driven car. Just did cam belt change and oils in engine and gearbox (febi, recommended)