LG · Laundry · WM4000HBA · Owner's Manual
This is described as water hammer. It is caused by household plumbing moving or flexing when the washer valves shut off, and it is not a washer defect. The manual suggests water hammer arrestors, or lowering very high household water pressure.
Source: LG WM4000HBA Owner's Manual, extracted pages 46-48
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Troubleshooting Overview
Your washer has an automatic error-monitoring system that detects and helps diagnose problems early. If the washer does not work properly or does not work at all, check the items below before calling for service.
For more detailed information or videos, LG directs you to the troubleshooting page at www.lg.com.
LG WM4000HBA Owner's Manual, extracted page 43Operation Problems: Leaks, Detergent Dispensing, Filling, and Cycle Behavior
This section helps you troubleshoot common washer problems such as leaks, detergent not dispensing correctly, filling issues, pauses during a cycle, and the washer stopping or not starting.
Banging noise when the washer is filling with water
LG WM4000HBA Owner's Manual, extracted pages 46-48This answer is only published when it has a reviewed answer status and a source citation back to the manual text.