Agreed that it sounds like something settling out from your beer. Could be a light film yeast, but that usually takes some time to develop. How long has your cider been sitting around, and under what conditions? Film yeast looks, well, filmy on the top and doesn't have much of a taste, in my experience, in the early stages. The cure is 100ppm k-meta as soon as your confident that it's film yeast. Much easier to tell with a photo.