* Fuel Leak: This is the most concerning possibility. A leak in the fuel lines, injectors, or fuel pump can lead to fuel spraying or dripping, potentially causing a fire hazard. The sound could be the escaping fuel under pressure.
* Vacuum Leak: A leak in the intake system (hoses, gaskets, etc.) can cause a sucking or hissing sound. While not directly related to the *delivery* of gas, it can affect the *mixture* of air and fuel, leading to poor engine performance and potentially damage.
* Faulty Fuel Injectors: A faulty injector might be leaking fuel, causing a hissing or clicking sound, especially when the engine is off or just starting.
* Fuel Pressure Regulator Problems: A malfunctioning fuel pressure regulator can cause excessive fuel pressure, leading to leaks or spraying.
* Loose Fuel Cap: While less likely to cause a significant noise, a loose or damaged gas cap can allow fuel vapors to escape, potentially leading to a hissing sound. This is less likely to sound *like* gas getting to the engine.
What to do:
* Do not ignore this sound. Fuel leaks are extremely dangerous and can lead to a fire.
* Do not start the engine if you suspect a significant leak.
* Turn off the engine immediately if you hear the sound.
* Have your vehicle inspected by a qualified mechanic as soon as possible. They will be able to diagnose the exact problem and perform the necessary repairs.
The sound itself doesn't give enough information for a precise diagnosis. A mechanic needs to inspect the fuel system visually and with specialized tools to pinpoint the source of the problem.
