I have swapped over to a solid axle, and think I have a bad bearing some where inside the rear end. I had some bald tires on, which led me to suspect the tires were causing the noise, but I just got new ones put on and the noise is still there (I also put on a set of friends tires to rull out a bad tire). It sounds like a whirring noise or a humming noise from 35-55 mph, but you cant hear it above or below those speeds. Would it be a bad axle bearing or perhaps a carrier bearing? The noise is there on decel or accel with clutch in or out, so I think I can rule out the gears.