Welcome Richard and congrats on the CT.... I too came from an Accord ('06) which was one of the best vehicles I've owned -- I was so impressed I had to have another Accord and decided on the CT for more versatility.
I saw your question and answered over in General Discussion and wish you luck with finding the answer. I'm pretty sure it's tranny related since it's similar to the sound my CT makes and my other Honda automatics have made.
I've heard other Hondas do this so I'm thinking it's normal tho it is a resounding clank and can be disturbing.
Colin.