Is it the Smart Hub 2, as that has a relay inside which will click if you lose the broadband signal from the line.
See if the lights change colour when you hear the clicks.
Is there any noise on your phone calls? Dial 17070 and select option 2, there should be no noise between the announcements.
have you tried a factory reset by pressing the recessed button on back and holding until lights flash?
remember when hub restarts to switch off smart setup
have you turned of smart setup