I know this sounds odd, but since it isn't bike or pedal speed related, I'm down to the odd.
Is it at all possible that you're feeling your own pulse or heartbeat? If not, consider having a friend join you on a ride to that good section of pavement and switch bikes.
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Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.