A 6212 would have the 6260 or 6261 pump, both used the same drive unit, 6200.700, if the wavebox was made before early 2006, it could have the older 6100.600 drive unit and these would click when the brakes started to wear loose. I would confirm the pump model and drive unit type and that will help me narrow down the cause, likely it just needs a new drive unit assuming it is otherwise functioning normally.