In 3 of the 4 cars I maintain I cant hear before and after differences when changing viscosities. But with the Volvo's twin cam 20-valve engine, which sounds like a sewing machine anyway, I'm confident it's less noisy at a warm idle with the 0w-40. After the oil change I drove a few blocks, pulled back into the drive, opened hood with engine running and noticed the difference. In any case, perception becomes reality.