Could be a rear wheel bearing go bad.

hmmm, well now hopefully that's what it is, as I thought about that being a
bearing as well and am hoping it isn't the gears as I really don't have the
money or time right now to have those replaced.
thanks for the reply.

Look for a flowchart that gives a diagnoses of rear end noise because you
can pretty well pin it down by documenting under what conditions the noise
occurs (ie:coasting, under load, turning etc)

Here is one example:

http://sonoma.unclewebster.com/lc/bus/625/

FWIW running the car with the wheels off the ground isn't really an
accurate test (unless the differential sounds like a meat grinder!!)
because you are unloading the gears and there is always some minor slop
and noise in there that will quiet down when the wheels are on the ground.

Wheel bearings, U-joints and of course tires are the most common cause of
noise/vibration coming from the rear ends.
Check your fluid level as well.
Is it a limited slip differential?
If so (I don't know about Ford??) it may require an additive.

Don't discount a bad tire because a shifted belt will cause an awful sound
that is hard to localize and it can happen even on a brand new tire.

Rear ends are pretty reliable and when they fail pinion/ring gear/spider
gears, most, not all, but most times it is catastrophic, meaning you will
have parts all over the place <bg>!

Try the obvious first, move tires around or better yet cycle the spare
into the loop for testing purposes.

Was the car loaded down with luggage?
Sometimes U-joints only fail(make noise) when the car is loaded in the
back (passengers, luggage etc) because the angle of the shaft changes and
aggravates the joints because if the car is normally driven with one
person at a time, the joints kind of get *happy* in that position.
Usually you'll get a vibration though.
My Impala SS is classic for that problem.

Good luck

--------------------------------------------------------------------------------

well found out what the problem was anyway. sorta anyway.
got a guy who works on rear ends to come out yesterday and look at the car
and after going over it. (samething I did) and came to same conclusion that
I did gears are fine axel bearings are fine and (hopefully) pinion bearings
are ok. that its the carrier bearings that are bad and he's going to start
work on it Monday sometime.
Charles