SER gas tank whine

[Dave]

Its unlikely that the fuel pump is making the noise after the engine is shut
off. Nissan fuel tanks hold pressure during normal operation... there may be
an internal vent line or valve that is leaking and making the whining noise.
Using the OBDII scan tool, the dealer should be able to determine if the
tank is leaking pressure. It sounds like it could be the onboard fuel vapor
recovery system is making that noise. Is it hot where you are? Hot fuel
tends to generate a lot more vapor and pressure which could be precipitating
the noise. let us know how it turns out.
-dave

Have to agree with Joe on this. Sounds like a fuel pump, but it shouldn't be
running after the engine's off.
Look in your fuse box, and pull the fuse after shutting the car off.
Still hear the noise?