The most common causes I have seen for cogging.
(not in any particular order)
1. Firmware- some of the older versions were not very smooth on startup, update to the latest version for best performance.
2. Connections- check all of the connectors very closely, including battery, motor, and all receiver connections.
3. Overgeared- this can cause cogging and overheating, which will permanently damage the motor.
4. Overweight- Castle's Sidewinder and CMS-36 motors are designed for lightweight 1/10th scale machines. Heavyweight SC style trucks are too much for these smaller motors and ESC's. Unless of course you have the Sidewinder SC system with the Neu-Castle motor.

I also see many motors that have been overheated and never have good startup quality again.
If the cogging is minor it can often be "tuned out" with start power, throttle curve, timing and punch control.

There really is no mystery around brushless motors; heat is your only real enemy with the Castle motors. If you get it good and dirty you may have to open it every year or so to clean/replace bearings. But if it stays pretty clean, and you dont overheat it, it should last for many years without any maintenance whatsoever. I recently sold a Mamba Max system (original) that I bought the day they were released from Castle. To the day I sold it, it ran just like it did when I opened the box, with no maintenance at all. Get yourself a temp gun if you dont already have one. Keep it under 175F and it should last and last.