What sound may indicate a pressure leak in an aircraft?

A hissing or squealing sound coming from the window, door, or exit may indicate a pressure leak in an aircraft because these areas are critical points where the pressurized cabin connects with the external atmosphere. If there's a breach, air from the cabin can escape, resulting in a distinct hissing noise. This sound suggests that the integrity of the pressurized environment is compromised, which is important for the safety and comfort of passengers and crew during flight.

The other options do not specifically relate to pressure issues. For example, a loud thump from the overhead bins may indicate a loose item or a malfunction in the storage compartment, but it does not signify a pressure leak. A consistent whirring noise from the engines is typically normal and related to the operation of the aircraft, not to cabin pressure. An alarm sound from the cockpit is generally indicative of other system malfunctions or alerts unrelated specifically to pressure leaks. Understanding the sounds associated with pressure integrity is crucial for flight attendants in ensuring the safety of everyone on board.