Motor Failure on Hexacopter

I am building a Hexacopter using Simonk 30A ESCs with Hobby Power 2212KV920 motors powered by a Pixhawk 2.4.8. I am only able to get half of the motors to spin up properly. The other half are spinning very rough and are making a kind of ratcheting sound. Does anyone know of any potential solutions or reasons why this could be happening?