On Tue, 14 Jul 1998 08:53:01 -0700 Vernon Craddock said:
>  When entering the wake of a Semi Truck while a cross wind is present, I hear
>the following:
>whap       whap    whap  WHAP SLAM!

well, even though you THINK it's coming from the rear, sounds can fool you.
mine does that and i tracked it down to the FRONT headlight grill. yup.
the turbulence of some big trucks, especially those with round tanker
trailers or car-carrying trailers ("portable parking lots"), causes the
bottom of the grill to flap around.

>Only thing I can figure is that it must be the rear air vents getting back

if someone sitting in the back can hear it behind them, then yeah, it might
be the rear vent grills. they do get loose over time.

but i'd bet on the headlight grill. :)

joel