Generator Noise Evaluation

Whenever a generator is producing current, a slight high-pitch noise can be heard and is completely normal. This noise is referred to as "magnetic noise" and results from the rotating magnetic forces which induce mechanical vibrations within the generator. The generator typically has several machine resonances throughout its operating speed range. Magnetic noise can be distinguished from other types of noises in that it becomes loudest within small RPM ranges, and is more pronounced at lower generator speeds near engine idle. To identify magnetic noise, disconnect the 4-way connector at the generator. If the noise is magnetic noise, it will not be heard with the generator disconnected. Other bearing, belt or interference type noises will likely continue when the generator is not charging. Whenever evaluating a magnetic noise complaint, be sure to test the vehicle's battery. A damaged or discharged battery will cause an excessive load on the generator, thus increasing the amount of normal magnetic noise.