Chevrolet Equinox LT 06 Differential

Hello, I just had a problem with my car. It started making
rattling noises, like 2 pieces of metal rubbing against each
other. I took it to the mechanic and they told looked at it,
the problem was that the "differential" is broken and that's
what causing the noise. Now, my question is, how is that
called? They told me differential but I think it has another
name because I keep looking for it online, to buy a new
one, but nothing. They told me it controls the AWD in the
car. Can someone help me please! I need to know. I'll try
posting a picture later. It's at the end bottom of the car.
Between wheels