Bad hum vibration noise

[93formula]

My car, since it has been running has this really bad deep hum vibration noise coming from the front center. It sounds like a rotational vibration. Now the car has a Shep tranny, so I'm eliminating that. The driveshaft is tight and has only minimal play in the carrier bearings. I first thought it was my exhaust, but I have made it impossible to be that. The transfercase is full of fluid but is old fluid. I don't think the noise is the transfercase. But I'm open to suggestions, any ideas?

 

[93formula]

Here is and update on the situation. I replaced the transfer case fluid withsome new stuff. The old fluid was black and has a grey fog to it. I'm assuming that is bearing wear as their was hardly any fluid in it I would say about 1/4 quart or so. When I replaced it I went for a drive and the nosie was exactly the same. Now the noise will only happen when the car is in gear with the clutch out. Clutch in and in gear it won't and in neutral it won't. So, to me that eliminates the clutch and the motor. The tranny I say is a possability, but I doubt that Shepard with as much as he does this would screw up but anything is possible. Transfercase, driveshaft and rear end. The latter I dount because I have checked everything with the driveshaft and the noise isn't coming from the rear. Any ideas on what else the noise could be coming from.