I'm back in the states and wanted to give you an update on the woodpecker living in my Rocket. I pulled the plugs this morning, as suggested by Rocket Scientist, and am relieved to say that they all look good and consistent across all cylinders. I thought about pulling the cam cover and checking the timing, just to be sure it didn't jump, but given the way it's performing, I think that is very unlikely.
For now, I'm going to assume that I'm just being overly sensitive to the new sound since adding the K&Ns. Rather than user error, a case of "user paranoia" is probably at play. Maybe the rock concerts of my youth have made the higher frequencies of the "chirping" that everyone talks about less prominent to me, and the intake valve noise reverberating in my helmet that much more noticeable.
Btw, while I was under the hood this morning, I changed the fuel filter (see photo). Would you say that it was overdue? At 27K I'm sure it was the original Triumph filter, as the previous owner made no mention of ever changing it.
Afterwards, I took her out for a long test ride. She truly does run better than ever, despite the woodpecker that I will just learn to ignore.
I appreciate everyone chiming in with ideas and support. I really was worried that I was trashing my bike based on that darned sound. Many thanks to you all!