OK ... I just got my 2014 Santa Cruz Tallboy LT. It is great.... I have noticed that when I go down hill and shift to a higher gear to go faster...that there is a creaking going on on what seems to be the rear cassette or derailleur. It does not happen until I get to shifting in the higher gears..... it gets louder as I get closer to the 10th .... what can that be?