I guess the first question is whether or not it does it when stationary or moving only. This will rule out things like wheel bearings and the like.
Next ask your mechanic to take the serpentine belt off to see if it is a belt driven component making the noise.
From the sounds of it, as mentioned above, if I had to guess I would say it was the pulsation dampener on the ABC pump, which presents itself very similarly. My advice would be to drive it as little as possible. I had a problem with my pulsation dampener which eventually lead to the main hose out of my ABC pump to rupturing.