Went out for short cruise without ear plugs and noticed winning noise, it only happens while on 5th gear, not 4th or 6th. checked tranny fluid, was OK.

its 06 FXDI with 24K miles.

Any idea???

 

I remember reading somewhere that 1st and 5th are straight cut gears and can be noisy? Try a search on noisy 5th.
CB

 

Its normal. Don't worry about it. It is just telling you that gear is stronger than the others. The sound is the byproduct of making the gear stronger.