LG · Laundry · WM4000HBA · Owner's Manual
It is usually caused by plumbing in your home, not by a washer defect. When the water valve shuts off, your pipes can move and make a banging noise called water hammer. A water hammer arrestor can reduce it.
Source: LG WM4000HBA Owner's Manual, extracted page 43
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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.