Hello Topcat and welcome from Virginia. I have a 2014 R3T with 66K miles on it now. Whenever I have noticed a symptom similar to what you describe, I too check the tires. If inflation is not the issue, what about tread? Is there any cupping starting to show? Under inflation exasperates this, thus I run 2 psi over the max and get longer life from my tires.
Is one side more worn than the other? Many roads have a slight camber which causes the tires to wear on one side more than the other over a few thousand miles. In this case, turn in is noticeable on one side and not the other.
Have you noticed any leakage around your down tubes? If so that may be part of the issue.
Has the bike been down? Bent parts or frame members may be the culprit.
Good luck in finding your real cause and do let us all know what you discover.