I have a 2000 F150 4x4 that has a poppin/knocking sound in the right frontend when I drive over rough pavement/ground. I changed the idler arm
that seemed to be slightly loose but the knock is still there. Any ideas as to what may be causing this?

 

Check your lower ball joints. They will make a popping noise when going over bumps.

 

would that also be the case when you start to turn the steering wheel, like it may have a slight amount of slack in it?

 

check your tie rod ends too depending on the mileage. i don't know that they'd make much noise, but you'd feel some slack in the wheel.

 

can you tighten those up, or is it once they are loose, they need to be replaced?

 

Once they are loose they need to be replaced

 

would that cause a front end wobble at highway speeds say 50+?