i beleave its from the cancelation of the sound waves and the pressure your subs produce. when u open your windows ur letting sound waves escape before the opposite wave meets it. i cant really explain im pretty much a dumb arse. check out this site
I thought i was the only one that noticed that!!//content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif//content.invisioncic.com/y282845/emoticons/crazy.gif.c13912c32de98515d3142759a824dae7.gif
Depends on the car. My car has bad aerodynamics (Chrysler LeBaron) When the windows are down, the wind coming in is loud as hell! My stereo is louder and clearer with the windows up.