My charger also started to keep some little abnormal noise, so i check'd the oil and got out about 90ml of oil.
Putted in all i had on my shelf of GM supercharger oil (160ml maybe) and the noise went down. No visible leaks anywhere and its been spinning only about 20,000 miles, so wonder if there has ever been correct amount. Ill have to get some more and fill it to proper level and follow up.
Just to suggest every supercharger owners to check that matter.