I have a Shimano Sora, 8-speed, GS for triple rear derailleur and a Shimano CS-HG50-8, 8-speed, 12/25 freewheel. The problem is that the guide sprocket grinds on all rear sprockets regardless of front sprocket position. I have adjusted the B-tension screw to almost every possible point without any improvement what so ever. I have already checked the high and low limits as well as the barrel adjustments on the rear derailleur to rule out any other cause for the noise (grinding).
