Generator Noise Test

Noise from a generator may be caused by a loose drive pulley, loose mounting bolts, worn or dirty bearings, defective diode, or a defective stator. A high frequency whine or magnetic noise may be heard at full output. This is a normal condition.
Perform an output test in order to help distinguish bearing noise from the magnetic noise, also called a whine. Refer to Generator Not Operating Properly. Generator Not Operating Properly
A shorted bridge diode will reduce output to approximately 1/3 of the rating and have a growling noise when at high load. It is also helpful to listen to the generator with a moderate load (engine cooling fans or headlights on) in order to determine if there is a bearing or magnetic noise.
Trouble in the charging system can be detected by the following conditions:
^ The charge indicator does not light during bulb test, or does not go out after the engine start, or comes back on while the engine is running.
^ An undercharged battery as evidenced by a yellow dot in the hydrometer or spewing of electrolyte from the vents.
^ An overcharged battery as evidenced by spewing of electrolyte from the vents.
If an undercharged or overcharged battery condition occurs, the following procedure may be used to check the generator drive belt tension.
1. Visually inspect the accessory drive belt for damage or looseness.
2. Inspect the charging circuit electrical connections for damage or looseness.
3. Perform the Generator Electrical Test. Refer to Generator Not Operating Properly Generator Not Operating Properly