So, last night, riding home from work, when switching to my largest chain ring, my chain fell off. Now, I know that is due to a poorly adjusted limit screw. I can fix that.
However, instead of stopping immediately to put the chain back on, I decided to just coast until I stopped. Not pedaling allowed me to feel a bump.
It feels like I'm riding on a rumble strip, that is very spread apart. It feels like one bump per rotation of the wheel. I feel it in my butt, so I believe its the rear wheel. I know its not the road, because I intentionally rode slow / coasted on quite a few different roads (maybe 1/2 mile) and it occurred on all of the roads, some of which are quite new roads.
While pedaling quickly, I don't notice the bump - probably because of all the movement that's going on involved in pedaling. The bump feeling is more pronounced when I am rolling faster (coasting down a hill), which leads me to believe it is based on rotations of the tire. I do not need to be pedaling to make this happen. I do not hear a noise, I just feel it.