Thanks man, I've tried two different RF boxes (sega, nintendo) with the same results. I also was able to tap sound directly from the sound chip and got the same result.
Sound is there, but its extremely overwhelmed by buzzing and other noise.
I've been wondering if its something in my home's wiring, which would be weird because I don't get this with any other console. I've been thinking about trying it with a battery attached for DC power instead of the transformer.