If I stay in a gear for an abnormal amount of time w/o shifting, say staying in 2nd gear up to 4000rpms, the boost gauge makes a rattling noise... It's odd and only happens every no and again - anyone have a clue?

I don't know where yours is mounted (I'm assuming A pillar), but are you sure it's not the gauge holder rattling against the car. Or maybe a loose screw or clip behind there. Just a shot in the dark, but that's really all I can think of. Can't imagine why the gauge itself would rattle.