I know it’s the injection pump. When I pump the fuel filter, the injection pump quits ticking.The issue is not so much why it sounds as why it is heard. I have a 1HD-T of 1994 and the ticking was driving me mad since I bought it. Then I had a head gasket issue and had to take it to a workshop. Amazingly, the ticking was much, much muffled when they delevered the car back to me. Of course I asked the mechanic.
Go to the floor below your engine. You should see a thick foamy thing, gasket-like, behind the engine, between it and the gearbox. It comes that way from the factory, but is normally discarded and not replaced whenever a mechanic removes the engine from the car. That thing is what muffles the ticking noise. There are many 'whenevers' in a 31-year old car, and mine was without it. The mechanic had a new one around, and installed it. Unfortunately, I am not able to locate the part No. But next time I go to the workshop I will learn it and post it here.
Cheers