Today I noticed a weird feeling coming from my drivetrain. Since I just flipped my hub to fixed a couple days ago, I'm hoping it's just something that fixed gear bikes do instead of something more serious that would need work.

I don't feel it when I'm actively pedalling, but when I'm slowing down and not really pedalling, just letting my legs spin, I feel a slight rhythmic...something with each turn of the pedal. Wish I could describe it better. Anyone know what I'm talking about?