I missed the booster pump part and I was thinking generic pump troubleshooting. I never dealt with a booster pump situation. The noise you describe sure sounds like air in the system though. Any air bubbles visible out of your returns or the polaris itself? It doesn't take much of a leak to let enoigh air in to mess things up. Right now I don't have any other ideas.

Anyone else out there with some words of wisdom?

Al