Rapid knocking noise at WOT from rear of car

[John]

98 Legacy Outback
2.5L N.A.
5MT
4.44 final drive

Under hard acceleration, I get a rapid knocking noise from the rear. I've jacked up the back and checked all of my lateral links, struts, wheel bearings, u-joints, brakes, etc. Everything seems to be ok. The only thing I did notice was a torn inner boot on one of the rear axles, however it doesn't have any play in it when I try and move it by hand, so I don't think this is causing my noise.

I've even put it in slick mud to see if my rear tires will still spin, (thinking it might be a rear diff problem) and they spin as they should....but in slick conditions I don't get the knocking noise. I guess you can say it happens at WOT under load.

Has anyone come across anything like this?

 

[ZachTTLM]

get your car in the air but dont support it by the rear diff. Once you have it supported on jackstands take the jack and jack up on the rear diff. See if there is alot of extra play there. If all the other components see good, you may have ripped diff support bushings.

 

[SSJBaku]

+1 cousins 98 Legacy had this same problem and it was play in the diff support bushings