Horrible vibration!!

[BufSabres]

Here's the problem and I cannot figure it out. When I drive below 45 MPH, it's a smooth ride. As soon as I hit 46 MPH, there is a vibration accompanied with a humming noise. The faster I go, the vibration becomes worse and the humming gets louder. It reaches it's peak at approx 65 MPH and my floorboards feel like a vibrating foot massager at a shopping mall, and a subwoofer playing a solid bass line. I have replaced the wheels and tires, struts and springs, subframe spacer bushings from Z1, my drive shaft is a 1 Pc from Z1, approx 15,000 miles on it. I thought it might be the wheel bearings, but the noise and vibration does not go away when I sway left and right on the freeway. Has anybody experienced anything like this and if so, please tell me what the issue might be. I'm running out of ideas on what the problem might be. Just getting frustrated!!!

[Ace2cool]

Center carrier bearing on the driveshaft. try to wiggle the DS from under the car. if it moves, it's bad.

Options: replace carrier bearing (difficult and puts failure-prone parts back in car) or swap to one piece DS.

[BufSabres]

It's already a 1 Pc driveshaft

[nissanfreak12]

You said you replaced the tires. Where they with new or used tires? Did it make the vibration before?
Recheck the tires and make sure you have no abnormal wear patterns.

On thing you can do is jack the car up and grab the tires at a 6 oclock and 12 oclock position and try and wiggle the rim/tire. If there is any movement, you have a bad wheel bearing. Its not rpm related, its speed related, does it change pitch when you swerve?

[BufSabres]

No it doesn't change pitch. It is still loud when in neutral gliding at 65mph, but is louder under acceleration/deceleration. I'm going to jack the car up in a little bit to check the tire play. It also happened with the old tires and wheels. I replaced them with new ones thinking the tires were the issue, but I was wrong!! LOL!!

[nissanfreak12]

Have you checked the fluids in the diff or even trans? Can you tell if its more in the back or the front?

[NolimitZ32]

Only other thing I can think of that hasn't been mentioned are the diff mount bushings (not sure what they are actually called)

[BufSabres]

I figured it out. As I was underneath the car looking for anything out of the ordinary, I noticed the 4 bolts holding the driveshaft to the rear diff were loose. Problem solved (with thread lock of course!!) that's one of the few times a problem was fixed and it didn't involve spending hundreds!!!!