I had the same sound on my CU2 Lux Navi Auto. My dealer said the same thing at first that they could not reproduce the sound and could find and thing wrong!
I made a recording on my IPhone for them and played it for the service manager. He then told me that he had another Euro with the same problem and was waiting on Honda Australia for advice. I was told to wait and they would contact me when they received advice from Honda Australia!!
A month later I contacted my dealer as I did here from them and was told Honda was still looking in to it, but my dealer asked me to leave the car over night and they would try and reproduce the sound.
The service manager told me he heard the noise and would be requesting a new auto transmission and torque converter for my Euro. Within a couple of days they received the go ahead from Honda Australia. My Euro auto transmission and torque converter was replaced and I have not heard the noise since. All this was over about 6 months going back and forth to my dealer.
I think this noise is a known Issue at Honda Australia and I would get your dealer to contact them .
My warranty has been expired on May. Been dealer before expired warranty for replace rust sunroof and explained a noise with video clip but they said they couldn't heard noise from my car. And if I bring me car to dealer with noise they will ask replace cost. Isn't it ?