Here's a good ticking video.. kind of.. Sounded like it was coming from the collector area, that's what was so deceiving about it. .
I'd almost put money on it that it's the pick up tube O-Ring.. I'm that certain.. I've been thru this.. You're about to go thru it too.. Read thru that thread on tech.. it took a SOLID MONTH of throwing parts at the fukin car to FINALLY get it.. was that damn $3 O-Ring. If I'm still around when you do it, get the water pump off and I'll do the oil pump for ya. I've got the tricks to do it without dropping the oil pan. (skinny fingahs and a "Custom 10mm wrench.. lol )
I bought two of those O-Rings. one for the install, and a second for insurance. Sorry, I meant the #7 cyl lifters are the first to get oil, the last one in line on the driver's side. It's something to do with the ported oil pumps. Or else your o-ring got pinched somehow, or blown out or god knows what. I'd replace the oil pump while you're in there. What year was the car/engine again?