My tour bike sure has a shimmy with the full load on the back, so no riding without a hand on the bar. Doesn't stop me from doing anything else though. Maybe the head angle is too slack, 70/ 70d.
And unloaded doing my downhill speed runs to 45 mph, it has a weird hum from the front somewhere at about 22 to 33 mph, tires likely.
With my old Raleighs I would use my knees against the TT the few times they went fast.