Buy some new bushings if you've sprayed them down with lube! Pull the trunk upholstery out at the sides of the seat thru port and you'll see the rear strut towers! I found tightening the shaft nuts down while holding the shaft cured the problem! Most owners have tightened until the shaft starts to spin and they call it quits! Just hold the shaft(at the flats) while you tighten the nut, to bottom out or expand the rubber bushing slightly wider than the concaved cup washer! You don't need to jack it up... just climb in and get comfortable! Good luck.....

 

Thanks bud, I have the same noise coming from the back on my car as well. 4 different mechanics could not find this noise. And yes it is embarrassing when driving over bumps.