When it opens, stored fuel vapors are drawn in from the charcoal canister to be burned. This is a "duty cycle" valve meaning it turns on and off. The on-time vs. Off-time percentages change to vary the average amount of flow. If it's clicking, it's working.
There was a recall on them many years ago. The charcoal in the canister broke down and could work its way up the vacuum hose to that valve and plug it. The recall involved replacing both parts and blowing out the lines if charcoal was found in them. I performed about 50 of those recalls and never found a bad canister.