It seems that during fall/winter my car's exhaust seems to either carry more, or be louder somehow. In the summer, it doesn't seem that loud; but in the winter, it seems really loud. I've noticed this both in traffic and alone on backroads in the sticks, so it's not just a lack of or presence of ambient noise. I notice it with the top/windows up or down.
FYI I am completely sober, this is just something I've thought about here and there. Have a Lancia for your time.