Volvo went from a flat tooth belt to a round tooth one, with a noticeable reduction in noise. Every little bit helps.

Read up on all the troubles Nissan had with the Leaf, with no engine noise, every other little thing became irritating.

I recently replaced my wireless Sennheiser headphones with really good Bose, and I found a lot of the vids I was watching on youtube have really horrible sound. The Sennheisers hid this well.