Rotospectre

Hey everyone, I tried many searches for this, but all I've been able to find were threads on 2nd and 3rd gens, and I have read them. Anytime I drive my car, ('83 GSL with the LSD rear end) I get this intermittent rattle from the rear end. The odd thing is that I only hear it when I'm constant on the throttle, not accelerating or decel, so I don't believe it's the U joints. It also makes no difference weather or not I'm on a rough or smooth road. It almost seems like the axles have play in them. I have read about broken diff mounts in 2nd gens, but nothing about FB's. Any ideas? Thanks in advance!