Coolant fan

A picture might help us understand what's happening. Most radiator fan assemblies bolt into the core support. If your Jetta has a part of that assembly that extends to or bolts into the engine, then movement by the engine may be why it keeps snapping. Or broken motor mount or dampener may allow excessive engine movement. Pop open the hood and have a helper start the car, and watch for movement by the engine. Have the helper shift into drive and reverse (keeping their foot on the brakes) and again watch for excessive movement.