I had the same issue with an 03 700. Over the summer, I replaced all the bearings in the suspension and drive shaft. Also did both clutches, and replaced chain and sprockets.
First ride out and there was a whine between 25-40mph. It wasn't there the season before, so it had to be something I changed. Took everything apart again but could find nothing wrong. To me it sounded like the chain case, but really hard to pin point. At one point I was going to put the old gear set back in and see what happened, but never got around to it. Rode it like that for 600 miles without a problem.
I read that the metal roller on the tensioner can make a lot of noise.......?