About a week ago I replaced the stock rubber drive shaft center support bushings on my '05 LGT with solid billet aluminum ones from Torque Solution, purchased from FredBeanParts.com.
http://www.fredbeansparts.com/media/catalog/product/cache/1/image/5e06319eda06f020e43594a9c230972d/t/s/tscarrierbearing_1_1_1.jpghttp://www.fredbeansparts.com/media/catalog/product/cache/1/image/5e06319eda06f020e43594a9c230972d/t/s/tscarrierbearing2_1_1.jpg
While I'm recently just out of the 1000 mile break-in on my new build engine (ringlang failure of OE pistons) and still have not fully thrashed on the new engine, these did seem to add to the solution of eliminating the infamous "growl".
These are not a single solution to the problem. As anyone who has followed or read through the entire thread knows the fix is to eliminate as much of the built in "softness" of all of the drive train and rear suspension bushings. Remember, the Legacy was designed to be a "near luxury" sedan so the engineering, especially for the NOAM market, focused on limiting NVH as much as possible, thus the cushy bushings.
Other mods I've made to remove slop, and in the process eliminate the "growl", include:
RalliTEK poly AT mount insert
Beatrush rear differential front member
Whiteline rear differential bushing stiffening inserts
Spec-B rear lower arms (stiffer bushes than GT)