Take the exhaust manifold heat shield off, you'll probably find a crack in the top of the manifold. Depending on how large the crack is, the ticking diminishes as the engine heats up & expansion closes it up. If not this, then a bottle of Wynnes Lifter treatment in the oil will usually fettle a sticking lifter, if not then the affected cam would need to be removed to gain access to the guilty lifter. This would need new cam cover gasket, new cam pulley bolts & new lifter/s. All DIY-able and if not causing you too much stress, could probably wait until the cambelt needs replacing, then much less work involved