I had a swishing noise on my bike recently. It was driving me crazy, until I found out the rear wheel was ever so slightly rubbing against the frame when I was riding. Problem fixed with that one! Have you checked every part of the wheel? Maybe when you're sitting on the bike, the weight causes the tire to rub but it's not apparent when it's on the stand, since there's no weight on the frame when it's on the stand?

For the crankarms, when was the last time you changed the ball bearings? Do you think it could be time to change them out? Have you greased up the bottom bracket? Could that be the problem?

Just some conjecture and speculation for you to consider.

Koffee