I think my car stereo was louder then the cars at night due to the fog slowing them down.
Ironically I understand that it was the fog that caused the problem. Sound travels further in damp air (or through water) and that meant that folk slightly further away were disturbed during the night.
And yet, the cars ran behind the Safety Car during the fog at a much reduced pace. I'd woulda thought the A43 created more noise.