Update
Hi All, Well, I found the problem. The rim had been damaged, looks like a head-on curb strike and was repaired, actually very well with only the slightest dip in the braking surface and a slight .2 mm decrease in circumference for about 20 mm. There are no cracks or other stress related damage.
When checking runout using the inside of the rim there was actually a very slight dip, which gave the appearance of a hop as the rim returned to normal. Very little work was required to true the wheel.
Brad