Mine seems the same - earlier than 60 though, higher revs in all gears really. definatly not the fan, somthing to do with accelerating so maybe pressure leaking somewhere, breather pipe, exhaust (just ghad new system so if it is it will be by the manifold as it was doin this before the new exhaust too). Its really annoying me now, might take it to a main dealer if i can't get to the source