The clicking noise you are hearing is probably the 'alarm' when your temperature is more than 5 degrees off what the thermostat is set to target. You can disable this alarm by hitting 'Enter' then the '-' button until you reach the screen below and then hit 'Enter' again to disable.
I am running many VE's on my pets (Not a 300x2 though) . I have never had an LED appear dim--I would definitely check the temps to confirm it is working properly--the VE-300 also has a compartment in the back that comes with a spare fuse: If all else failed I would change that fuse to see if it made a difference...
Over the years I have noticed an issue with some of their LED's malfunctioning: they will stay on consistently (as opposed to blink) even if the thermostat has reached its target temperature. I have cross-checked their readings with my own temperature measuring equipment and it seems the LED light display is not accurately displaying the output to the heating elements (thankfully). I have temporarily (months) resolved the issue by unplugging and then re-plugging in the thermostat and they will usually return to normal function when they 'reboot'.