Anytime you install any aftermarket product on the exterior of your vehicle you are changing the aerodynamic flow of air around the design of your vehicle. This is not limited to just the installation of racks but any product like window visors, roll bars, brush guards, etc. The following paragraphs give you some helpful tips on what to do if you experience any excessive wind noise or whistle after installing A truck rack or van rack.
Specific to vans:
Reread through the installation instructions enclosed in your parts bag. Be sure to check to make sure all hardware is fastened securely. All Cross Tread Gutter Mount Van Racks feature a PATENTED Clamping System. The Clamp will actually adapt to the contour of the gutter and not let go. Make sure the carriage bolts are tight. Cross Tread Industries has actually hoisted a FULL SIZE DODGE VAN off the ground with an overhead crane attached only to the Cross Tread ALUMINUM 660 on the vehicle. The gutters of the van withheld the weight and the rack didn't budge. Periodically check to make sure all hardware is securely fastened and rack is in good repair.
After you have properly installed the rack and all the mounting hardware is tight, be sure to seal all areas where tubes telescope. This will not only prolong the life of your rack by disallowing moisture to enter inside the cross bars (especially on steel models), it will also block wind, reducing whistling and keeping everything tight and secure.
Nine times out of ten, simply moving the front cross bar forward or backward a few inches will dramatically effect any noise. If the cross bar is in direct flow of air coming off the windshield, move the front bar out of "the line of fire".
If the problem still persists, try changing out (switching) the front bar with the rear bar. Be sure all hardware on the actual cross bar is going in the same direction (towards the rear).
Cross Tread Industries Inc. ladder rack products are designed to fit the majority of vans and pickup trucks on the market today. Due to the vast number of engineering changes by the automotive manufactures, a "perfect" fit cannot be guaranteed on all vehicles.
A NOTE ON THE ALUMINUM 660: The length on the formed diamond plate cross bar (1 7/8" x 2") on the Alum 660 is 60". If your van is shorter than 60" , you will have to trim the bar, if it is longer than 60", there will be an area where the insert will show (usually 2 inches or so). It is not unlikely that this will only occur with one bar as most new vans have tapered rain gutters.
Ford bars are designed to be used as a center bar (third) on full size 1992 and later Ford vans. The weld location on these bars is 1 inch lower to compensate for the domed rain gutters on these vehicles. Some of the new 99 full size Chevrolet vans also require these bars.