Mystery pump like noise in rear end

[Tribeca Mystery]

I have an intermittent noise which sounds like a pump switching on which comes from the rear end of the car.
It randomly switches on and will stop when the engine is turned off. It does not seem to affect the performance of the car but changes sound with excelaration. A mechanic suggested it was the fuel pump, so I had a new fuel pump installed however the noise is still there (still intermittently). I have been to a Subaru dealership and played the sound to a mechanic and he does not know what it is and suggested I try a forum. Any ideas would be much appreciated.

 

[Ecmbuster]

Mystery model year and engine?

 

[Tribeca Mystery]

Mystery model year and engine?

2011 Tribeca 3.6 R Prem Auto 7 seat.

I have attached some links for audio of the noise.

audio 1.m4a

drive.google.com

audio 2.m4a

drive.google.com

 

[Ecmbuster]

Place your hand on the tank. if it is the fuel pump, you should feel the vibration. An automotive stethoscope is a good tool to use.
Near the tank, there may also be a carbon canister, engine management may also attempt to purge the gases or pressurize the tank to "self check" for gas leaks.