check the obvious things first:
inner/outer tie rod (independently)
axle
upper and lower ball joints
any one of those things cause a knocking sound, some dependent on speed or angle of the wheel.
if a strut is bad they tend to sag and squeak in addition to feeling sloppy when you hit bumps.
BUT to your original question:
put the front end on jack stands and remove your tire, inspect the top and bottom "seats" of the spring, the should both sit in a grove in the metal base and top-hat of the strut itself.
while you're down there grab the brake rotor at 9 o'clock and 3 o'clock and push and pull and alternate arms pushing and pulling. I bet you find your rattle.. if you don't, it's the axle OR the last thing you want, the differential is having issues.
hope this helps.
