Can you take a closeup picture of that airplane.

I'm not even positive the black lump behind the prop actually is a gearbox. But it looks like one. A closeup might even show where the gearmesh can be adjusted.

If it is, the motor is usually attached to the gearbox with a couple of machine screws. The screws usually go through elongated holes. You move the motor so that it's drive gear meshes properly with the driven gear of the gearbox, and tighten the machine screws. If the motor gear isn't properly meshing, it will scream. Sometimes it's too tighly meshed and grinds. Sometimes too loose and usually makes a higher pitched noise, sometimes not. Depends on the gear materials and the cut of the teeth.