Thanks for the reply.
A better word is shudder. It is a vibration / shudder / chuggle from the front end, engine area that I perceive through the pedal / wheel as the seat is soft, as you say. There is no steering pull. It always only occurs at about 22 mph and stops at 25 mph. It does not occur during moderate to heavy acceleration. It is more noticeable after the engine is warm. It does not occur during coasting. It can be prolonged and made more noticeable by driving up a steady smooth hill at 23- 24 mph.
The dealer said that the mechanic felt the vibration. I was not in the car. It was attributed to needing a transmission update.
The new tires are Bridgestone Dueler H/TP-Metric BL 25/65R17 101H, which were actually a replacement due to flat spots on the original tires (car sat a long time on lot), a freebee from a Firestone shop, after the Dealer wanted me to wait to see if the flat spot fixed itself. These are the same brand and size, but a different, actually better higher speed rated tire. The tire shop should have torched them correctly. I have them at 32 psi with a dial air pressure gauge.
The vibration is not in sync with the eco light -- I cannot feel that transition. Not related to windows or AC. I am certain that it is not due to road conditions. It occurs like clockwork anywhere, however very mildly under most conditions.
I still suspect the tires/wheels but they have been rotated and rebalanced by Firestone. Honda service tech, while investigating thumping from flat spots, discovered that the car was way out of alignment. Dealer said this was a known issue from cars being very tightly chained down on rail flatcars during delivery from Ohio, and that I might hear more about it, never did. I wonder if this have damaged a wheel bearing or drive shaft? I asked a Honda tech about the drive shaft and he said that this would be more noticeable at higher speeds.
I plan to bring the car to another Honda dealer and have them check the vibration and also have the Firestone shop rotate (about due) and balance again and check for the problem. I've owned the car 14 months and has 13,100 miles.
Thanks for the diagnostic tips!