My guess would be that the bearings in the BB are in need of some tlc. I would do an overall on the BB and clean and relube the bearings. If its a cartridge BB a.k.a., New, then you can simply replace it. When your at the LBS getting the new BB, pick up some finish line chain oil for $5. It's worth it. WD-40 is as good as using salt water. It will actually get rid of the grease in your drivetrain, leaving it metal on metal which would significantly stiffen up the drivetrain. Honestly, i would bring it in to the Bike shop. You will be glad you did.