Bottom line is that some have the whine, some don't. My 07's 5th gear doesn't do it and doesn't have the rattle that many experienced. Those that do have it say it goes away after a while especially after changing to a syn gear lube.
Use Spectro 6speed transmission oil and you'll never hear it again. Here is a link http://www.spectro-oils.com/products/transmission/hd6speed.asp?products=cruiser I have been using this since I did the 5K service and I will never use anything else in my trans.
Not bad at all. The whining by some guys here is far more bothering than the one in my tranny. lol
I use Redline w/Shockproof and it quietened things quite a bit.
I can hardley hear it on my 09 Rocker, pipes and no windshield pretty much take care of that, on my previous 09 ultra I could hear it, but it actually helped remind me what gear i was in. Noticable but not annoying at all.
5th gear does sound different from the others on my 09 FLHT. Really not bad though. The only thing is with 6th gear being an over 60 mph gear you are in 5th a lot.