Hello again. I have two virtually identical 1998 rivies, both with over 120,000 miles. They both run rough at idle and 'knock' from the top of engine (e.g. Super charger, OHC, Valves, etc.) . Both cars are tuned, new belts, new pullies, one has new alternator & water pump while the the other a new A/C compressor. The supercharger oil level is perfect. I've had a good non-rivy specialist check out the superchargers for bearing noise and that is his best 'guess' - but I am not so sure because the knocking coincides with rough idle (much like the car is skipping or experiencing mild pre-ignition detonation).