Don't turn on phantom if you have sand in your motors.
The motors may not start and freak out the ESC. If they do, you will hear it squeal.
The squealing is from the polarities changing incorrectly. If you look closely, there is black foreign minuscule rocks (ferrite) in beach sand. This causes the outer bell housing magnets to "short" and alter its polarity. You will see between the gaps that the ferrite tries to bridge the magnets.
Unfortunately, the motors are pressed in and cannot be separated without damaging the bearings. Your best bet is to replace motors.
And if you cant...
In my scenario, it was holidays and I was 1000km from home and no hobby stores were open.
I took the motor off the arm and used an airhose from a mechanic. Use the air to move the particles down the bell housing. Then use tweezers and budge them out of the bell housing and then use tape to lift them off the magnets. Painstaking...