Which Chain? (Chains / Size / Width / Wear)

It does sounds as if the frame is having an affect: the noise is deeper and less metallic than what I was hearing.

Based on my own experience and yours, I can only suggest that some sprockets don't get on with the 1Z1:

• experiment with different set-ups until you find something that works with that chain;
  
• try a different chain;
  
• put some miles on your current set-up and see if there's an improvement.
  
  

I don't know what else to suggest, or what the cause actually is.