Generator is excessively loud or produces knocking sounds during operation.

Safety first: Turn OFF the generator, disconnect battery negative, and allow the engine to cool.

• Inspect mounts: Check all engine-to-frame mounting bolts and rubber isolators inside the Firman enclosure. Tighten loose bolts and replace cracked isolators.
• Check exhaust system: Inspect the muffler and exhaust joints for cracks or leaks. Replace damaged gaskets or muffler.
• Evaluate fuel quality: Drain and replace low-octane or contaminated fuel. Use the fuel grade recommended by Firman.
• Listen for internal knock: If a deep metallic knock persists, shut down and have a technician inspect internal engine components; continued operation can cause catastrophic failure.

Do not ignore persistent knocking or metallic noises; internal engine repairs may be required.