Increased engine noise/road noise and decreased MPG?

2012 Prius 3 with 140K miles. Within the past week or so, there is now a noticeable increase in noise that at first I thought might be road noise, but now I think that it is engine or transmission noise. The sound frequency, and to some extent the volume, changes smoothly with the speed of the car. Higher MPH equals higher pitch and somewhat louder, too. It almost seems like the RPM's are too high and the tranny should drop into the next gear, but is this a thing with an ECVT? It's not a rattle of any kind, and I don't notice any difference in response from the gas pedal. Also, we're in the middle of a 1000mi road trip and the MPG's have dropped from typically 51mpg to 45 mpg. What should I suspect?