Compared to when you first get a specific car, etc, I can see that knowing your car better with time means
you'll perceive it as less quiet then before. "Familiarity may breed contempt".
On the other hand, if you hear clicks, thumps, rattles hot or cold, those are likely real
issues to look at.
With time and big mileage, every engine gets a little looser and produces more overall
noise!