Exactly how bad would you think B&M rattle would be? 
  
Here in Taiwan, I rode Insane Speed at Janfusun and it had a little bit of headbanging in the second flat spin. 
  
But on Scream! at SFMM, the Zero-G was just plain rough for me (maybe not Arrow/Vekoma rough)  but maybe I just haven't been on enough B&Ms to know how smooth a B&M should be. 
  
Are other B&M looping coasters much smoother than Scream! and Riddler and whatnot? Or is "Scream!" pretty much what you should expect from a B&M looper?