Do you have an unmodified vehicle, i.e. your suspension is factory standard?
If so, your front axle is probably hitting the bumpstops, as your front springs will have probably sagged to the point where there isn't much gap between the rubber bump stops and the axle.
You need new springs to cure this bottoming out problem or perhaps try a spring spacer, which you can fit to you existing springs to give your front end a slight lift.
Lawrance