Alright guys I just started trying to get rid of this vibe/noise I'm experiencing at higher speeds when on the throttle and coasting.

Here's my drive line. FLT Level 4 4L60E, stock drive shaft with a newer rear u joint. Stock 10 bolt with 3.73's (gm gears). Car is lowered. Hose mod on stock springs in the rear, QA1 front's set to match height. Yank torque arm relocation crossmember with poly bushing and stock torque arm. Also using a Energy suspension trans bushing and not sure if it matters, but I also have a edelbrock adj. panhard bar (rear is centered) BMR solid lower control arms with UMI relocates.
Never noticed this vibe/noise until I lowered it. Everything is good until about 90 then all hell breaks loose until 125/30. Noise is a very loud roaring that is somewhat felt also. Noise/vibe is also there from the second you let off the throttle until you coast back down to about 80. Noise seems to slack off at 130 (haven't had enough room to go over that) The sound of it is much worse than how it feels. I also haven't noticed this noise when making a pull with the cut out open.

I noticed that before I tried to correct anything at 125 the speedo seemed to bounce around, then fling down to 130. Didn't do it tonight after I made the changes below.

First steps I've taken:
Pulled car onto 4 post rack and visually inspected d/line angles. Damn thing is parallel from pinion to trans. Check with angle finder, 0* on both ends.
I did notice for the first time (I'm an idiot) that the Yank relocation crossmember lowered the torque arm a considerable amount from its stock location on the tail housing.

Second step:
Removed the metal spacer on trans bushing. Drove and noticed an improvement. Angle is about 1-1/2* at the trans and pinion.

Third step: Removed d/shaft, greased u-joint, reinstalled 180 from where it was. More improvement. Still audible, but actually liveable/less concerning.
Now when coasting after running up to 125 the noise is far less noticeable UNTIL it hits 110. Comes on very suddenly and goes away just as suddenly. Soon as it gets down to 105ish noise is gone.

Things I know that will improve the situation:
Driver's side rear tire has high road force and keeps wanting weight. I'm just waiting on my news to show up so I can replace.
Pinion does have some up and down slack, not a terrible amount, but enough that I'm going to have it redone and also all the bearings replaced at the same time.

Question. Am I going to have to go ahead and get an adj. torque arm?
OR can I try raising the back of the trans up since I have no more downwards adjustment? I didn't have time to try raising it tonight to see if that made things better?

What about moving the troque arm down? I could make new holes in crossmember to lower it, I have no room to take it higher.

My next step is to remove the tailshaft housing and double check the bushing to make sure its okay.

There also seems to be quite a bit of the slip yoke showing. Anyone have a measurement of how much of the yoke should be showing at ride height?

 

Wheel bearings immediately come to my mind when someone mentions a roaring noise.

The factory torque arm can start to bend approx six inches ahead of the rear, so you might check it out too. Bob

 

Thanks. I'll double check the torque arm again.

 

I had the exact same problem and it drove me nutts. Its your driveshaft. You might not be able to tell just by a visual inspection but its twisted. It took me days and days to find it. I hope this saves you some time. A stock driveshaft cant handle too much abuse, I'd suggest an aftermarket one.