Thanks for your responses...

Yes, I was wearing Chamois Butt'r, but I didn't add any after we started riding. And I put the Butt'r right on the seam that is irritating me.

It is the seam that is on the outside of the chamois, the one that connects the chamois to the lycra. Also, there is a seam running up the back of the leg but doesn't seem to be an issue.

Other thoughts? Thanks for your help. I can't understand why after four years of summer riding only now this is an issue. I did lose about 10 pounds during the winter, which I've kept off, but I don't think I can get shorts that are any smaller.