A friend and I were on top off Sgurr Breac NW Highlands, UK, OS grid ref NH158 711 (57 41’ 31”N, 05 05’30”W), altitude 999m on 10 July 2010.  A light  wind was coming from the south east at perhaps 12 -15 mph, the cloud was high and it was mostly sunny, temp around 15C.  We heard what sounded exactly like a flimsy plastic bag blowing from south east to north west and were able to track the sound as it moved across in front of us, about 2 metres away before it disappeared off the cliffs to the north.  There was no sign of leaves or dust moving in a vortex and the short vegetation didn’t move either.  The wind then dropped completely for a couple of minutes before returning the way it had been before.  What was this? Some sort of vortex?