Doubt it is the H spokes, but again, don't place anything in the fact that your car is in D, as it will not get a scheduled build date until it goes to D1 ( and as noted , that still does not mean it will be made exactly on that date ).
I have cars that have been in D status for over a month, since they are Red, and until the blacks get rocking farther, few were moved to D1. There are alot of red cars in D1 now, but not all , so you are in fine shape and until it reaches D1 and then jumps to E or beyond, you won't have a clear idea of when it is being built.