Driveline Noise at Highway Speed
 

Last year I noticed a small vibration and whirring noise coming from the driveline when I get up to highway speed. This noise sounds rotational and only happens when I am 1) In gear 2) above 65mph 3) pressing the gas. The noise is most prevalent when I tip the throttle slightly. The pitch of the noise increases with higher speed, not RPM. Happens in 4th, 5th, and 6th gear (didn't try anything lower). Upon initial inspection, I found my driveshaft to have lost a weight. I replaced the slip yoke and u-joints (got these from zfdoc) on the driveshaft when I balanced it. Put it back in the car and the noise is still prevalent at same decibel and pitch. Did not notice much vibration if any. Any other thoughts on what I should look at? Tailshaft bushing? Rear diff? Not sure how to diagnose or what to look for here.
1990 w/14k miles #973

Thanks,
Sean

Re: Driveline Noise at Highway Speed
 

Re torque rear hub axle stubs to 190 lbs. 36mm socket.
Retorque all wheels to 100 lbs.
Jack car up and are check all wheel bearings tight.

Has anyone messed with the car prior? I would look there too.