What is cogging?

[glassdoctor]

Could be radio glitching, could be a bad speedo...

Does it do it consistently under a certain condition, like accelerating from a dead stop? Or when it's far away etc? Does it do it after it's up to speed or only under accel?

"Cogging" is a brushless-specific glitch... that happens when the esc is trying to get the motor to start spinning, and it's "confused" and can't fire the motor correctly. Usually there isn't any cogging once the car is moving even a few mph. Once the motor is up to a certain rpm it normally stops.