I bought an aluminum one for my 96 and I didn't notice anything. I don't get bad vibrations, bought I hear a slight growning. I recommend high speed balancing your original to save cash, and have them replace U joints while their at it.
Another thing to consider is replacing the rear seal and brass bushing in the tail shaft. I just had my trans guy come over and change my bushing. There is a special tool he used, that I have never seen before. Now my yoke slides in much tighter than before. I'm sure this insures less noise/vibration too because the shaft has less up/down and back and forth movement. It's got to because had grooves in my old yoke and bushing, and it slid in and out very loose.
Another thing to consider is replacing the rear seal and brass bushing in the tail shaft. I just had my trans guy come over and change my bushing. There is a special tool he used, that I have never seen before. Now my yoke slides in much tighter than before. I'm sure this insures less noise/vibration too because the shaft has less up/down and back and forth movement. It's got to because had grooves in my old yoke and bushing, and it slid in and out very loose.