Alright, i'll try to explain this as best as i can because my buddy and I tried to replicate this on a rack at the dealership we work at and couldn't replicate it. The car has an M6 and when i'm taking off in first, (easy or hard acceleration) and then get ready to shift, when i unload i am getting this audible metallic sound like a bad u-joint. but then when we tried to replicate it on a rack, we couldn't get it to do it. we tried with the e-brake on to be able to load the driveline and unload it real quick. So i am almost wondering if it might be my differential? Any and all possible help would be appreciated.