You're reading too much into it (just a fun hobby, really).

Totally get what you mean about listening to the engine idle. In my experience, tools are great for codes, but your ears pick up the early weird sounds. My old Corolla had a tiny click that turned out to be a sticky valve, way before any light came on. Catching that saved me a big repair bill later. It's a skill you build over time, just paying attention. Scans have their place, but they don't hear the small changes.