Define what was actually stopped

Rotor stopped does not necessarily mean every actuator, fan or electrical function was inactive. Identify the available state evidence and the sources that could still operate. A nearby pump, fence or building can continue to create sound under the same weather. A stopped-state recording therefore describes a combination of remaining sources, rather than a guaranteed background-only or zero-machine-noise baseline.

Compare weather and observation conditions

Changes in wind speed, direction and microphone location can alter recorded sound substantially. Automatic gain can make two phone clips appear similarly loud despite different source levels. A sound absent in one stopped interval may simply have been unobservable then. The comparison is more useful when it isolates a repeated feature under reasonably comparable conditions and retains uncertainty about sources that were not monitored.

If a reported tone persists while the rotor is stopped but an auxiliary remains active, that auxiliary becomes a candidate source rather than proof of ambient noise. The review should identify which functions were still present before using the interval to exclude machine-related causes.

Use the result to select investigation

A tone persisting with the rotor stopped weakens a hypothesis requiring rotor rotation, but may still involve another machine component. A disappearing tone supports investigating rotation-linked mechanisms without identifying one. Ask a qualified reviewer which physical or acoustic evidence can resolve the remaining source. No MARSTON stopped-state behaviour, automatic stop function or acoustic limit is assumed; the operating and access decisions remain governed by applicable instructions.