First off, defective wheel bearings don't make a "squeaky" sound. They sound sort of like one of those big mud tires do going down the road (low, growling sound), and it's constant. So disregard that. Check all of your basic brake foundation and see if you can visually find the problem. Are you having any other issues, other than the sound itself? Is it veering to one side, rough steering wheel, etc.? Worst comes to worst, inspect the drive axles as well as the intermediate shaft, bearings, etc. Like I said, it's not a bad wheel bearing cuz that would be constant.