I had something similar last year and it turned out to be a collapsed bearing.
Bearings on the utes are easy enough to replace. Each axle is held in place by four 8mm allen key head bolts.
Get the axles out and take them to a workshop that has a hydraulic press. Either use the press to press the old bearings off or use an angle grinder to cut the collar cage off and then smash the bearing cage off with a hammer and chisel. Then press the new bearings back on.
When removing the collar, bearings, seal and retaining plate, pay attention to the order and which way each item faces. Take photos with a camera or phone.
Taxi workshops use: "Timken 4827 Wheel Bearing Kit" because they last the longest. Do a search for Timken 4827 on eBay. Take the axles to a taxi workshop if you can (do some Google searching) - they do this all the time, so will know what they're doing and will be cheaper than most places.
With the axles out, you'll also be able to see the diff oil. If it looks bad then drain and replace the oil - you'll need a 10mm allen key for the filler bolt. Make sure that you can remove the filler bolt before draining the diff oil.
Why mention the diff oil? Because if it's a collapsed bearing then there will be pieces of bearing cage floating around in the diff oil. Ideally, you would remove the diff backing plate and flush the whole diff/axle tubes out with petrol/kero/whatever to ensure that there are no pieces of metal left in there.
I put together a photo guide recently:
http://www.fordforums.com.au/showthread.php?t=11418260