That is a strange problem. It came, then it went away as fast as it came!

My first thought was wheel balancing or ball joint but those type of problems should be constant. Not come and go.

I'll second the alignment idea. I recently bought 4 new tires. When the tire store went to do a 4 wheel alignment they discovered that 2 bolts were frozen on the rear trailing arm so they couldn't adjust the rear toe. This explains the unusual wear on the outside edge of my old tires. Again, check your tires/wheels and consider a visit to a good alignment shop.