Gas burner is "clicking" - how can I stop this?
I bought a used cooktop off ebay once that did the same thing. I discovered it to be one of the dials which was catching in the ignite position (although the dial didn't look depressed).
Give the dials a good workout when the ignitor is clicking away--you might release the switch.

That fixed it for me and I soon identified the culprit dial. Every so often the constant ignition would come back but I'd just smack the guilty dial and it would stop.