Which of the following is a sign that a septic system may be malfunctioning?

Unpleasant odors coming from the area is a significant sign that a septic system may be malfunctioning. This can indicate that wastewater is not being processed properly and is escaping from the system, which can lead to more serious environmental and health concerns. A properly functioning septic system should not emit any foul smells, as it is designed to treat and contain wastewater effectively.

In contrast, healthy grass growth near the system can sometimes occur over a properly functioning system, as nutrients may leach out into the surrounding soil. Consistent water levels in the tank could indicate that the tank is not draining properly or may be full, which could also suggest a potential problem, but it’s not as immediately indicative of malfunction as unpleasant odors. Cleansing sounds when it rains are not typically associated with septic systems and may not provide reliable information about their functionality. Thus, the presence of unpleasant odors is a clear warning sign that should prompt further investigation into the septic system's health.