What could be causing a front end popping noise?

Most likely the CV axle/joint The rack could be the culprit too but unlikely What you may want to do is look and make sure the rack is tight and not moving around i have seen racks come loose and actually shift side to side to check it have someone turn the wheel while you are actually watching the rack as the wheel is turned otherwise i would go directly to the CV axles When the cup that hold the bearings wears out The bearings tend to make popping noise especially when turning the wheel Its cause the cup is so worn the bearings bounce around in the bearing cup ( not the actual names of the parts but close enough that you may follow what what i am saying ) So 9 out of 10 times its a well worn CV axle that's making all that racket Okaty then if you replaced all those parts then that popping is something out of alignment and its re-aligning itself during first drive .Check your motor mounts , strut towers and the bushings that are on them also is everything TIGHT better check loose sway bars , loose or broken motor mounts ( trans mount too if applicable)either something is loose even the retainer nut on the end of the CV axle even a broken strut rod can make that popping noise Its something that is realigning itself in my opinion making me think something is loose or a broken strut or motor mounts

Unless you've replaced all of those parts you don't have a clue if they are making the noise! Have a mechanic put a set of "Chassis Ears" on the suspension and track down the noise instead of guessing!

I had a truck that did that. It was the rack and pinion assembly. The mounting bolts holding it to the frame were not tight enough.

Have you replaced the shocks?

Maybe your bumper is loose somewhere.