Just in 4th? Or all gears? All of the evo sporties I have owned have had whine in 4th gear, but they changed the gears for 06 up, I don't know if it carried over to the XB or not. With that said I have a 04 XB and it is surely a quieter trans than the Sportsters
Primary chain tension ok? My father had a big twin evo, Fat girl or some silly bike like that and it had terrible noise coming from the primary, turns out the primary chain and sprockets were toast.