I was pretty sure the goldfinches were pulling off the coneflower petals, and now I have proof! The video may be a little shaky, but the evidence is rock solid.
Dear Mr. Goldfinch, I love your presence in our garden. I even had you in mind when planting all the coneflowers here. I hoped you'd enjoy the seeds. But hey, what's up with pulling off the petals? You don't even eat them. If you please, I'd greatly appreciate it if you'd keep to the seeds, and leave our coneflower petals alone.
Of course I realize you'll most likely ignore this request, but I had to get it off my chest anyway. Thank you.