I just put in a LS1 driveshaft and Im getting a roaring sound that seems to just be there if I accelerate up to 70-90 and let off and let it coast, just letting the car hold its self back. Also crusing around 70 I get it alittle noise. Im not getting much vibration that I can feel but if its the driveshaft balance can it hurt anything running like this?

 

Check the rear end where the drive shaft connects to it.
Make sure it does not move in around.

(I think you might need some rear end adjustments or bearings.)

 

what adjustments do you mean what bearings? I have 4.10 gears going in May the 2nd so the pinion bearing I guess will be changed then

 

Ok I put the stock shaft back in with a new rear u joint and Im still getting the roar so I stuck the LS1 back in with a new rear U joint still have the noise. One question, the stock shafts old rear U joint would barely swivel from side to side, the new one swivels freely. Is it suppose to move freely or be kinda stiff? Im begining to think its the rear wheel bearing or the rear end.