Does the clicking noise stop as you roll up to a complete stop and the SC shuts down? On a quiet street try that. If the click disappears with the SC whine-stoppage, it will be EZ-er to diagnose. If it still clicks at idle w no SC, the exhaust idea from above is something to look at. A quick exhaust check might be a good thing to do at a local muffler shop that is trusted couldn't hurt.