Smarthub 2 disconnected then rebooted by itself about 20/25 mins ago, as it was about to turn to blue again I heard a couple of clicks from it, blue light came back and no more clicks, heard similar when I first installed it, I imagine this noise is normal in this instance? Also never noticed any random disconnection on the old hub, would this be a software update perhaps?
If its anything like the earlier home hubs (HH1,1.5 and 2), then there will be an internal relay which controls the function of the phone socket on the back of the SH2, and also the connection to the DECT base station within the home hub.
During a restart, its quite likely this would operate then release, which is why you hear the clicks.
On the old home hubs, that relay connected the incoming line, to the socket on the home hub, if the old Broadband Talk service failed. This ensured there was always a phone connection.
Unfortunately the relay was a common cause of failure, as the contacts fused together when there was a storm.