quad yaws to the right or left without touching the sticks

my qx95 hovers great and then all of a sudden it just yaws to the right usally or sometimes to the left and it doesn't mater if I have my hands on the sticks or not, I can be just flying in a strait line and all o a sudden it just spins around and comes at me or the other way you can never tell, I have 6 quadcopters and this is the only one that does this and its brand new, any help would be great