I got possible tappet noise in my Sierra Cosworth 4wd, it kind of started after the car stood for 3 weeks without being used. It makes very audible clacking or ticking when it's cold, for about 5 minutes. Before, it only made the noise for like 30-60 seconds and it wasn't as loud. When cold, the noise fades when giving slightly revs, but also it might be the engine noise over the ticking. The noise drastically reduces after around 5 minutes so it can't be rod bearings? Also when the car is hot it makes a bit of the same noise but it's much more silent and sounds like any other Cossie in YouTube videos. Also on hot starts, it makes the ticking sound for few seconds after it quietes down? How come the noise started after the car wasn't used for 3 weeks? I changed new oil after that, same 10W-60 Castrol Edge FST and it didn't help. The noise seems to be coming from the head.

My cold starts are around +10-25 celsius temperatures. Car has 168 000 km on the clock. One weird thing is, that the noise has never been audible in first ~5 seconds. It only starts after few seconds after starting. I'll take videos when I can, but when cold it sounds quite like the car in this video, 1:25 ->