They can and do leak down overnight (or longer) and tick when cold in some engines and can be very normal especially in colder climates. Subaru and Mitsubishi and VW all have TSB's on this issue. The fix is to drive them at 3K + rpm for 5 min. VW says as long as it goes away (one some engines like the old 2.0) consider it normal (they have had issues since the Vanagon days when they put hydraulics in them). Varnish can also cause this due to sticking but that noise is usually constant and doesn't go away.
Some Subaru engine will rattle like marbles in a can if let sitting for a week or more, a horrible racket, give it a good run and it will go silent, the lifters bled down and are air bound, 100% normal for these.
Of course with most engines this is not normal and cracked exhaust manifolds are a common issue as is high pressure fuel pump cam lobe erosion on some engines, secondary air pumps and some other issues can all make similar noise. Finding the root source can be a bit of a pain as some of these systems only run for a short time when the engine is cold.
Then, I suppose I am fortunate.
I've never owned one of those cars...