I've read in a few replies including a couple to my own posts is that it could be the vacuum pump making the noise. I still have my "tick" after putting in an other set of injectors. The car does seem to run much better now and has more power, idles smoother and doesn't stall soon after starting it cold if I let my foot off the pedal.
Additonally I've gone through and readjusted my valves and even checked my chain for stretch the guides and tensioner for wear. Too my pleasant surprise I found virtually no chain stretch on the car with over 225K miles on it.
I think I'm probably overeacting to my problem.

So, how many miles have you driven this since you first noticed the noise?

Have you done the compression check?

Metal in oil?

Although I can't hear the engine, it is starting to sound like a possible rod bearing problem. It knocks until the oil pressure pumps up in the morning and it knocks when the engine is hot. If this is the problem it may not be too late yet to repair with new bearings.

Also, I would want to rule out the vacuum pump as the cause before I jumped into the bottom end.

Good luck.