I know mine isnt a b&m shifter, but a clone...
I believe I know where the rattle is coming from...
look at the 6th picture and on...
You see where the two shafts mate up and there is a hex bolt and locknut connecting the upper and lower shaft together...
This is where I felt obvious movement, I tightened the locknut 5 turns and it still has play, enough so that when I move it back and forth I can here it hitting metal...
So at high rpm's I could see the rattle coming from this area, just my observation, I dont have it installed yet...
USPS delivered a few goodies today! - Short Trow Shifter & Magnetic Drain Plug