So I took into vines in Guilford and they sent one of their techs out on it. They came back and said that they could feel the grinding noise and they would book in for 2 days to do some tests, Unfortunately they can only book in at the end of September. I did think that only riding 1 up while in pillion mode might have been the cause as the bike expects more weight and hence the grinding, this maybe the case however vines thought that it was worthwhile taking it in to look at nonetheless. Will update when I have an answer.