I thought the TSB on this issue stated that the dealer should replace the Transmission mount, not the motor mounts. I had the same issue....vibration and then a moaning sound....and the new tranny mount cured it.
2009 G8 GT - Premium and Sport Packages
Mods - Roto-Fab Intake, BMR Front and Rear Sway Bars, BMR RTAs, BMR Steering Rack Bushing, BMR Rear Cradle Bushing Inserts, and Cortex Tune. Summer set-up - 18x9.5 TSWs - Cooper 275/40/18 RS3-S, squared, LS3 Cam, Kooks Mids....and others.