This is amvery common problem on the Epson 700 and 750 scanners. They are reflections bouncing around due to the multiple layers of glass. One way to allevite them is to tape the negs emulsion side down to the lower platen with thin hinging tape. I lay my negs down and tape one edge down, then i place a strip of tape on the opposite edge film rebate, and stretch it out and down onto the platen. Then change your scanner silverfast software to scan the Full film area with the little frame overlay they supply, and go from there. Its a way to get the best results i have managed with this scanner short of a better scanning film holder, even then reflections can still cause issues.