[s-cars] Humming after shut off

[Bob Frizzell]

S-men,
Like the old Buffalo Springfield tune that goes something like "What's that sound, everyone look what's going down ..." (Hap, Dave, you guys should be old enough to remember that) after I turn my ignition off (sometimes) I get a hum from the rear (of my car, not mine).  Sounds like the fuel pump to me.  Is this an indication it's thinking about packing it in.  It's intermittent - I haven't been able to get back there and locate the sound and "the barracuda" (that would be my wife) has refused to lie under the car as I drive in the garage (and I'm a good driver).  Any BTDT?
Bob
93 S4