Are you running a "add a light" rail or anything? I was looking at the 4.2 which basically has the extra hanger for the second light. If your 4.0 is noisy without venting or a 2nd light, I could imgaine that extra weight would only make it worse! Damn...
How loud is it compare to a 6'' inline fan? Could you hear it outside of a garage, that is my real question?