I suspect that you may have a contamination problem "somewhere". Oil filter, oil pump, oil pick up and fouled pushrods are all possibilities at this point. Does your "ticking" come and go and correspond to your oil pressure drops directly? To me it sounds like something is working under pressure and intermittently failing. If the ticking doesn't correspond to drops in oil pressure, I'd check for good electrical contact at your oil pressure sender just to eliminate that as a possible source of future annoyance. Changing the oil and filter might be a good place to start. have a good close look at the used oil to see if there might be something odd about it,