I guess I should elaborate a little more, the OEM bushings up front are pretty much solid with an insulator. The ES I received from Coz were a softer compound up front than the others received in the same kit.
Due to the extra movement, the diff was knocking the lower bracket up front.. If you remove the bracket you should be able to see if or where it's contacting.. If that's the cause, another option to OEM or grinding 'may' be to space out the bracket so it sits a bit lower.