There are four orange and black rubber inserts that the hard drive sits in. One side has full circles and the other side has half circles. (The other side of the half circles are located on the hard drive bracket that was previously removed).

The new upper case may not have these inserts. Be sure to remove them from the old and insert into the new.

The inserts are easily pried out with a spudger or a flat tipped screwdriver. They are not glued in, but instead have notched sides to hold them in place.