Wouldn't a new softail have the exact same noise? Where would buying a new bike fix that?

 

I've got an '08 FLSTC and my 5th gear is smooth and quiet. Maybe it is '07's only.

 

Since you're talking about spending some serious cash to fix the problem why not spend a little to see if you can help quiet it some? There are about five different synthetic gear oils that can be tried. Why some will quiet one bike and not another is kind of strange but that seems to be the case. Use Mobil 1 76w90 for 500 miles. Stay in fifth at 55 or higher. Then change to Mobil 1 75w140 and go another 500. If it's still noisier than you want go to Redline for 500 and then to Amsoil for 500. Your experiment with all these different gear lubes might help someone else with the noise. Cheaper than buying a new gear box or bike and might be an interesting experiment. You'll at least get good at changing the tranny fluids.

 

07 FLSTC and have a llittle whine also. at 1k put n syn3 and stage 1, did help but was never a problem anyway, the pipes does cover it up and I also notice that if I ride without windshield it is all but gone and I have to really listen to hear it.
At 10K service went with formula+, it helped, and at 13+k I dont hear the whine at most speeds, If I think about it and really listen I can hear it sometimes.
Could be one of those things to that the more it bugs you the more you hear it..

 

My 08 Train is good, I don't hear any noise in 5th, with the exaust and wind, hard to hear much else. I also don't use it till I'm over 55 mph.
At 1000 miles I had syn oils put i the whole bike and the trans shifts so much better than before.

 

my noise has gone with the use of bel-ray gear saver.
http://www.belray.com/consumer/product.fsp?pid=13637

 

Changed out the Tranny fluid for Red Line Heavy Duty 75/140 and did it make a difference. The shifting is smoother and the 5th gear noise which previously stayed loud all through the RPM range, now is only heard at 2100rpm and lower. Once I am above 2100 it disappears by at least 90+% and if I was not aware or listening for it, it would be impossible to hear. Actually the whole bike sounded different...the pipes seemed louder and throaty and the engine/tranny noises were as if muffled in cotton. The Red Line Tranny Lube is DAMN GOOD!!!!

FXDSE2

 

My 5th sounds a lil' different, but not enough to bother me. Mine's an '07.

 

07 fatboy here. I have never heard this so-called 5th gear whine. I do use mobil 75w90 gear oil. maybe that's why i don't hear it.

 

My wife didn't hear it on her 08 Deluxe either, until I put a windshield on it. Neither of us have any whine, least we don't notice it. Both have the rattle/clatter in 5th.