Hi guys .as of a couple of months ago my Harley sportster1200 xlh has been making a strange whining noise only in 3rd and 4th gears .. it is really faint in third but when I am in forth and get to about 3000 rpm the sound kicks in :/ and then goes around 4 then back around 5 again and gets louder in higher revs on certain throttle positions .I am stuck I have pulled out the gear box and checked it over it seems fine and everything else in the primary seems OK too no visible wearing ect its hard to tell but I'm positive it is coming from the gear box or primary. Does anybody have any ideas I'm so stuck .mechanicaly it is fine motor seems to run well and gear shifts are fine .I'm stuck