Hi There, I've just recieved my mail order Oliv G&D strings after recurring problems with rattling Velvet Garbos. Can anyone tell me what the felt rings are for...? There seem to be two on each string.... I can only assume they must be used at the nut and the bridge somehow. The Garbos sound great, but two different D strings have started to develop a strange rattle after a couple of months of regular gigging. Has anyone else come across this? Thanks, Mark H.