In my experience valve clearances will reduce over time as the valve seats recede into the head. I've never had an issue with valve clearances on car engines but it's common on highly strung motorbikes. You cant hear a tight valve.
Yep exactly. Usually in alloy heads exhaust valves recess back into the head, decreasing clearances and making the car harder to start when warm and with a more erratic idle. Intakes usually seem to wear and can increase and be noisy, though they also can recess - they just usually don't as they don't get quite as hot.
In any case, in Australia under the capped price servicing schedule for early 2019 cars it was 6 monthly service intervals and valve clearances checked at years 2 and 4. Mine definitely were checked at years 2 and 4, and, in year 4 the rearmost cylinder did need the clearances tightened up (which was all covered under the capped price servicing schedule so no additional cost to me). I can do it, very familiar with what's involved since it's all quite similar to I4 motorcycles but with easier access to stuff, but much easier to have the dealer do it for me when I wasn't paying extra for it.
Post September 2019 cars get a 12 month/15,000 km service schedule with valve clearances checked in year 3 (i.e. at 45,000 km).
I will definitely check mine at year 6 when it's due. Not hard at all and you're 80% of the way in there when you've popped the coils off to chuck in fresh spark plugs anyway.
You absolutely won't hear a tightened clearance and they are the more problematic of the two directions clearances can go. You might notice the idle or harder to start issues when warm, though.
