I have recently noticed two white spots of discolouration on each lens of the Rift. It is the exact same size on each side, and does not appear to be on the lens, as they are in the exact same location as well, and cleaning the lens does nothing. They are less visible against a dark surface and more visible against a light surface. Can anyone advise on the nature of this, and possible fixes? It breaks immersion quite effectively, and is difficult to ignore.