I drive a 2004 ford Expedition XLT, The front

could be from worn tie rod ends, suspension ball joints , worn suspension rubbers and failing shock absorbers
take it to an accredited suspension service center for a complete check including the rear end as the front floating sensation could be from a problem rear end suspension set up and shock absorbers
I am well aware that every tire shop says rotate tires but in reality you just move a problem tire from one corner to the other, fail to see a wear problem develop in the tires ( indicates alignment or tire case problem) and costs 4 tires at a time instead of 2 which is not really economical as well
consider this front drive cars wear out front tires at the rate of 3 to rear tires 1 and I think you get the picture (rear drive cars rear tires 2 to front 1) or if there is a case problem with a tire it is lost in the rotation process and becomes dangerous on the road

Clicking Noise From Left Front Tire Area - F150online Forums

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Aug 11, 2001 - I have a clicking type noise comming from the left front tire. It does not ... I can really hear it when I'm driving beside a sound wall or the side of a building. ... the sound. (Yeah right!) ... Almost forgot: 1999 Ford F150 XLT Supercab 5.4 4X4. ... My 2000 4X4 had a ting ting noise coming from the left front wheel. Intermitent Grinding Noise on 2004 F150 4x4 - Page 5
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Your best bet is to go to a place that specializes in front ends,no big chain company,we have one here,they will check the whole front end out,may already know cause they may have repair one like yours before,plus all vehicles have a history,best not to start replacing parts,can get costly if your not sure,they will give you a free estimate.

Wheel alignment is out of specs. Loose front end parts

FRONT END SHIMMY AND SHAKING COULD HAVE A TIRE OUT OF BALANCELOOSE OR WORN WHEEL BEARINGS, WORN OUT BALL JOINTS,WORN OUT TIE ROD ENDS, FRONT END NEED ALIGNMENT.BRAKE ROTOR WORN OUT OR WARPED, MANY THINGS WILL CAUSE FRONT END TO SHAKE SHIMMY.

If your car is a all wheel drive you might want to check your maintence on your differentials that might be it.

Hi:
You can do a couple simple things to try to figure out what is going on with your expedition:

1) Inspect your tires on the front of the vehicle.
look for any signs of uneven wear or any differences between the two front tires. check the air pressure.

2) swap your tires from the back to the front : If the problem goes away. you need to have your tires inspected for problems, and balanced, if necessary.

3) check for slop in your steering. slowly turn the steering wheel and have someone watch the front tires one at a time. There should not be much play in your steering, meaning when you start to move the steering wheel, the tire should start moving very soon. Check both sides, and often you will narrow down the problem, after looking at the tires and checking for sloppiness in the steering. The most common cause is a worn out tie rod end, but if you don't find anything, usually an auto shop will inspect your car for free, and tell you what they find too.

check the idler arm on the steering drag link

Alignment has alot to do with the tires not shimmying.. Like zero toe setting. Loose componants like tie rod ends and the idler ar worn. You can ck for excess front end play by holding the front and back of the wheel and pushing and pulling on it, like rocking it. OR have someone rock the steering while you watch where the play is from underneath. By rocking I mean turn the steering wheel back and forth. Look at all th joints and pivot points for excess play, which is, movement not immediate to the rest of the steering system. Tire balance is very important. Wheel hop is a sign of a bad tire and it overtaxes the shock absorber. Shocks don't cause shimmy because they are a vertical movement controlA shimmy is lateral or side to side.Wheel balance weights must be spit. If a 2 oz. weight is needed to balance the tire, Oe once should be on the inside of the wheel and one ounce on the outside directly across from each outher.. Loose wheel brgs will cause shimmy, but they would not last long. Caster setting on the wheel alignment will also cause shimmy. Like on a shopping car. too much caster causes the wheel to start fluttering and is very hard on other componants. This may be why you have worn tie rod ends and a bad pitman arm. Worn control arm bushings and ball joints directly affect titre wear and can only be feltwhen the front end hits a dip and detected by side wear on the tire edges. Summary: replace the tie rod end and have the car aligned. Good Luck, -Ned_ sorry about the book

are the king pins worn .check all ball joints tie rod ends ect . 1 mm movement = up to 5 mm wheel alighn play ..also check shockies