I may be half asleep, or something.. and I apologize... but could you explain what the "n/s/f" is?
I'd suspect (since you can hear it more when next to walls and bridges, etc) that you should look in to wheel bearing/cv joint problems.
jack up one tire of the car.
grab the wheel at 9 and 3 oclock and push in and out (like you are trying to physically "turn" the wheel like the steering wheel would) and movement in that area can indicate a bad tie-rod, though usually not "grinding".
now, grab the wheel at 12 and 6 oclock. repeat the motion of flexing in and out. any motion indicates a bad wheel bearing. a How-to is in the Duratec Maintenance forum under the "read-first" thread.
repeat the process for the other suspect wheel.