This is an ongoing phenomenon, though it seems to have become more noticeable in the cold months.
My fuel system seems to be making a steady-pitched 'wooooohhhh' sound under very light throttle pressures, especially noticeable at 45-65mph. The reason the fuel system is suspect is that there ain't much else that COULD be making this type of noise, and I think I've eliminated the others. Also, I have a fuel pressure guage at about eye level, and have noticed that the sound syncs up perfectly with about thirty-one to thirty-three pounds of pressure.
Car is a 97, 4L60E car with bolt on and exhaust mods, electronic upgrades, and trans upgrades. Also present is the NOS drysytem with the appropriate booster pump. Let me add, the sound's occurrence is irrespective of the nitrous system status, and if I read the schematic right, the NOS fuel pump doesn't go 'active' until the system is triggered by the master and WOT switch. Also, I checked the routing of the fuel lines to see if there were any severe angles or elbows in which high pressure would cause noise, and couldn't find any.