shaking front end

[Twocollies]

I was returning home from a car show this afternoon when the front end started shaking. sort of scared me. I pulled over and checked the front wheels. I grabbed the wheel to see if there was any play. There was none. I looked around at the perches, drag link shocks. every thing seem fine. I started the model A up and drove the rest of the way home with no problems.
Has anyone experienced this and what could it be?