Motorcycle Repair: Gear Box Whine, left hand side, stator

Question
Just took over my Dad's 96 Sportster.  Late last fall he had the stator replaced to keep the battery charged and had only ridden a very few times until put away for the winter.  I noticed that; when not in a heavy pull, when decellerating, and when clutched and when coasting there is a whinning noise from the gear box. After talking with Dad, he indicated that it has always been smooth and quiet.  The noise typically drops out and everything is smooth around 20 mph and less.  I have not checked the fluid yet to make sure there is fluid but I was wondering if there was something that may not have been re-installed properly when the stator was replaced?  The noise is real apparent on the right hand side of the bike but can hear it through the left hand side at the primary cover.  When bike is in neutral, parked, and idling/reved the noise is not present.  

Thanks in advance for any help you can give.

Answer
First thing I would do is replace the fluid and then test ride it. When changing the stator you dont have to tear the trans apart. But the motor sprocket nut or the clutch hub nut might be loose. the chain might be to tight also
Good luck and happy riding
Mike