A lot of people have had problems with both the Kirban and Ripper using the stock knob. Wrapping the threads with pipe sealant tape and putting something (silicone) to reduce rattling under the cap seems to help. The best solution has been to change to an aftermarket knob.
If you're already using an aftermarket knob try to determine where the noise is coming from. Adding weight to the shifter will help if it's vibration coming through the shifter. You can use stick-on wheel weights and tie-wrap them for added insurance. If the noise is coming from the tunnel itself the only solution may be to add some sound deadener like Dynomat.
