GeorgS - thanks for the follow-up. Were you able to hear the loose inlet pipe when banging on the muffler?
My chirp noise appears to be acoustic vs. a rattling internal part. I can control the sound by blocking one of the outlet pipes and, I need to verify this, but I also think I was able to control the chirp as I was adjusting the idle mixture on a new carb. As I was richening the mixture, the chirp seemed to go away???