Yes it is true.
It makes some noise, at the time of calling as well as at the time of soft reset (restart). Update for HTC HD Mini Ring tone clarity enhancement also does not make any changes in this noise.
I think its antenna hardware make this noise, but also I observed that in some areas like my apartment basement and lift as well as highway tunnels, where most of phone does not show any operator signal, this phone works as well as you can make or receive calls in those areas.
This is just my observation, just try it and let me know.