From my limited understanding of how a supercharger works (oversimplified) it's just an impeller spinning inside of a venturi. It's not likely that sand was sucked into it. If that was the case, the sand would've gone somewhere & done more damage (not likely that it could have made it through the cylenders & exhaust system without clogging something up).

It sounds more likely that you have at least 1 bad bearing that is making all that noise. If the impeller or the venturi were damaged, you would be getting little or no boost.