terrible grinding sound

[BrianG]

That is loud, but it sounds like mostly the microphone being sensitive due to lack of background noise. When the ESC arms, it gives us a little more perspective and doesn't sound quite so bad. Personally, it just sounds like a mesh that is a tad too loose and the notchiness of the motor is making the teeth slap together. You could try a different pinion to get a slight change in gear geometry, but I think you're gonna have some noise like that no matter what, maybe not quite as loud.

My 1512/2d (same kv) sounds much the same way and it has been running fine.