Do you have any berry/bramble plants in the area? There are some borers that could be the source and they are equal opportunity borers within the Rosaceae.

It could be sawdust that a small bee or wasp is kicking out of a tunnel that will be used as a nursery chamber. These are usually in cut cane-ends but sometimes in the side of a green stem. The damage is so minor that I often leave them for the season if there is growth being supported above.

The other type of borers that tunnel way down a cane leave the frass behind them inside the hollow cane.

Hmmm. Thanks for the info! I do have a ridiculous raspberry patch about 30 feet away...I also have some open cut cane ends on this plant.
I re-examined the stuff I found; it isn't as gritty as I had first thought, but is a little shimmery - don't know how else to describe it.
I presume I shouldn't fertilize the plant if its not feeling well; should I pinch off its buds? I could spray with immunity booster, but would certainly prefer not to kill off bugs that aren't actually doing much damage.
I appreciate the help...

I doubt if the whatever-it-is would be the key thing. Sometimes plants will sulk in high summer. It's a new plant-- I would just be patient.

Thanks; patient I will be! Just nervous about my new babies...