We have a 1998 Outback Impreza Sport...and It seems if you really give it gas there is a noisy vibrations coming from the rear....And Idea what it could be?!?

driveshaft ujoints often cause this, probably the most common cause.

 

CV axles can as well - any broken boots back there? rears usually don't cause issues but *can*.

 

wheel out of balance?

 

can you describe it a little more? any noises at all?

does it get worse with speed or go away with any speeds?

If you let off the gas the noise eventually goes away then you can drive awhile before it comes back on...reminds me of driving on the rumble strips on the road but just coming from the rear

Sounds like it's dependent on speed. Try getting the wheels balanced.

If the vibration builds at about the same rate the speed builds, and keeps cadence with the speed, it's more likely to be a tire or wheel bearing or axle- something that rotates at the same rate as the wheels.

 

If it seems to build about 4x the speed of the car, it probably has to do with the trans-to-rear-differential drive shaft, which spins at about 4x the speed of the wheels.

 

I have seen the disappearing vibration you describe most often with driveshaft problems- U joints, center-carrier bearing or support, or a loose slider in the last section (which subes fortunately don't have).

 

 

Dave

Find my last posts on this site about the bushings I had to replace in the rear crossmember. Your problem sounds just like mine. I also found after replacing them that my front driveshaft universal was on its way out also. You need to have car on a rack (not running) with all 4 wheels off the ground and out of gear to check that drive shaft good as you turn it around by hand. Good luck

I think I found the problem...Universals are bad now bad thing is have to wait till Tuesday to get the parts

Yep guys it was the drive shaft and universals...Fixed it tonight took about an hour runs awesome!!!