Good points, thanks jtg!
So, the chatter happens when I point it down and I can feel and hear the back of the board vibrate, usually a lot in choppy conditions (runs with lots of tracks already there). It might be a weighting issue like you said, but it doesn't happen when I turn or go harder on an edge, so it might also be that I'm going too flat.
I am not comfortable on blacks yet, when it gets steep, I go veeery slowly. I don't falling leaf it, I do link turns, but I end up with the edge perpendicular to the fall line a lot, so that slows me down a lot.
From your post, I guess I should just save my money until I improve more. There will be plenty of time to get new boards in the years to come. So, thank you!