94 FSZ Blazer 6.5L TD grinding noise

I have a 94 full size Blazer and have recently had a strange kind of grinding noise when I am accelerating. If I accelerate slowly it won't do it but under heavier load it will make the noise. If I put it in 4WD the noise goes away. I think that narrows it down to the rear. I have some transmission fluid leaking from the front seal but that is about all else I have except for recent heavier leakage since this sound started. A friend suggested the yoke may have cracked which is something I haven't thought of. I'm trying to get a better idea before I just start tearing things apart for nothing.