They're sealed bearings - you have to replace them.  Cost is between $200
and $300.  You'll need a large (3/4" drive - somewhere around 1-11/16")
socket for the axle nut, and a 12-point 14mm socket for the hub bolts.  A
hub puller is nice to have, but not a necessity.

When you go to get the bearing (you can get this at a parts store, like
NAPA, AutoZone, etc.) they'll need to know if you have 4-wheel ABS or not.

Sounds like your brake pads may be getting low? Rolling element
bearings rumble, not squeek.

Check here...lots of info:  http://www.quad4x4.com/

    I had the same irritating noise in an '84 T-Bird.  Only the passenger side.
Only at slow speeds.  Only when next to a building or tall curb with the window open.
    Car drove just fine, no issues at all.  I repacked and adjusted the bearings.
More than once.  Checked the pads.  Checked everything I could think of.  More than
once.
    I was just about to decide to live with it.  Then I found a loose wheel weight
on the inside of the wheel.  Tightened that up, and the noise went away.