I tried searching for this problem and didn't come up with anything. Driving one day, I heard clanking noise from under the car, but it happened only twice so I didn't bother checking it out. Later, on a highway, when I went about 70 or 75 mph the car vibrates. The driveshaft seems to be intact and u-joints were replaced about 1k miles ago. I jacked up the rear end and put it in drive, the vibration is still there at 70 or above mph. I didn't try going above 85 because I didn't want anything to fall out. Could it be the transmission going or drive shaft needs to be balanced? Could wheels have something to do with it?
thanks for any help.

 

yes to all the above questions

wheel balance (most common), drive shaft, separated tire, loose steering /suspension parts are most likely suspects then brakes, internal trans internal diff, wheel bearings(although bearings,trans diff would possible make noise.

Easiest check the wheel balance then go from there

 

how could the wheel be knocked out of the balance? I think i eleminated the steering by having the driving wheels in the air and it still have vibration. Also what do you mean by seperated tire? All the tires look ok. I was driving nonstop for about 200 miles and it was fine for first 150 miles, then i heard clanking noise and last 50 miles or so i finished going 60 mph. What could've happened that knocked it out so fast without any warning?

 

Wheel weights can come off anytime for any number of reasons. Rub a curb loosening the wheel weights up then centrifigal force throws them off for example. A separated tire is when the tread becomes unbonded to the carcass, Most cases you will see a bulge in the tire and it will feel like you are sitting in a rocking chair sideways whild at low speed 20MPH or less, but in some cases it can not be felt till highway speeds. I have seen that cause a mis fire code in an OBD 2 car before even if the tire looks ok.

As I said before start with a wheel balance. It is by far the easiest to check and most common cause of a high speed vibration.

I wasn't suggesting the steering is the problem just listing possible causes of high speed vibration.