If you're hearing a rumbling noise consistently at night and it's not related to thunderstorms, there could be a few possible explanations. Here are a few common causes of nighttime rumbling noises:
Airplanes: Depending on your proximity to airports or flight paths, the rumbling noise you hear could be due to aircraft flying overhead. Airplane engines can generate low-frequency rumbling sounds that may carry over long distances, especially during quiet nighttime hours when other ambient noise is reduced.
Traffic noise: If you live near a busy road or highway, the rumbling noise could be caused by the constant flow of traffic. Again, during nighttime hours, when there is less ambient noise, the sound of vehicles passing by may become more noticeable.
Industrial activity: If there are industrial areas near your location, certain processes or machinery could produce low-frequency rumbling sounds that carry through the air. Industrial activities often continue through the night, so the noise may be more apparent during quieter hours.
Natural phenomena: While you mentioned that it's not thunder, there could be other natural factors causing the rumbling noise. For example, distant geological activities like volcanic eruptions or earthquakes may produce low-frequency sounds that can travel long distances.
It's important to consider the local context and environmental factors specific to your area when trying to identify the source of the rumbling noise. If the noise is persistent and causes concern, you may want to consult with local authorities or experts who can investigate the issue further and provide a more accurate assessment based on your specific location.