Wheel balance, tyre pressures, headstem bearings will give you a constant problem. You issue, sounds lik,e a dirty air problem.
This means minor turbulence from vehicles around you, and little wind gusts and so on. The ST has a lot of surface area that can act like a sail, the best thing to do is relax and go with the flow. The gyro action of the wheels means that the bike will self adjust for these things, (probably what you are feeling)