The caller said when he rolled down either of the front windows (the only ones that aren’t fixed in position), the volume from the speakers gets louder. The Car Talk guys said maybe that a venturi effect when the windows are lowered may be sucking more volume from the speakers. Lol. Is there a chance that this van’s factory radio unit may have automatic volume control? My sister has an almost 20-year-old Cavalier with it, so maybe Chrysler had this available too.
The fact that no one else has ever reported a similar phenomenon (regardless of size or type of car) points squarely at an automatic volume control installed in the radio. The reported draft increase, once any window is cracked open, is unrelated to the phenomenon, and simply indicates bad door panel insulation.
Here is a test to prove it: with the radio on at moderate levels (windows closed!), sing a steady tone really loud!
I bet, the radio’s volume will go up. (Early volume controls in cars did not yet have the secondary speed sensor feedback current systems have, hence, no reported increase in volume related to increased speed).
The caller mentioned during the call it was just a cheap-o am/fm radio, that’s probably why the Car Talk brothers didn’t consider automatic volume control to be related. But I agree, your test is worth a try for folks who have this problem.
I think we’re all in agreement about the automatic volume control thing. But the supposed increase in a “draft” coming from the speakers when a window is lowered and the volume increases is probably just an increase in the sound waves distorting more air in front of the speakers. In my car, which has speakers in the lower leading edges of the front doors, I can feel a “draft” on my left ankle while my foot rests on the dead pedal; with any increase in volume, and there is a commensurate increase in the “draft”.