I think that the noise in the area between the trucks cab and the bottom of the cabover is a direct result of the very high speed air due to the bernolli effect.
Some truck brands or models seem to have thinner or less rigid metal in that area.
In my opinion... as speed builds up so does the air pressure between the trucks roof and the bottom of the cabover. At some point the now very high pressure air pushes the trucks roof down, the roof "pops" back up... only to be pushed back down.
Over and over... faster and faster as the trucks speed builds up.
Now the roof of the truck would be Pulsing! Maybe even pulsing the air in and out of your ears.
This is my reason for thinking that the best solution will always be to install ihe wind deflectors as far forard as possible... to prevent the high speed air from ever getting between the trucks cab and the bottom of the cabover.
sleepy
BTW... any induced turbulance between the roof and the cabover might effect the trucks roof at lower speeds... there may be a critical point... where it sets up a harmonic (I need input help on this)
