We bought a 2014 Outback in August, and on two occasions have heard the same humming noise coming from the driver side rear wheel well when car is off. The car is garaged. Might be happening more, but heard it these two times.

 

We heard it recently and turned the ignition on, without turning on the engine, and the noise went away.

 

Any ideas as to what's going on?

Next time you hear it open the gas cap and see if it goes away.

Thank you. We'll try that.