The factory rear differential mount found on the Audi A4/A5/S4/S5/RS5 vehicles was not developed with performance in mind. Constructed of pocketed rubber, the factory mount allows the rear differential to move excessively during hard acceleration and driving. This excessive movement is responsible for the clunking noises and "slop" felt in the drivetrain during shifting and changes in acceleration.

In order remove excessive movement, Spulen designed a polyurethane insert kit to work in conjunction with the factory rubber mount. The polyurethane insert included with the kit installs in minutes on the rear differential mount and is secured between two precision billet retainers. Once installed, drivetrain movement is reduced and clunking noises are eliminated.