Someone told me a while ago depending on the shape and style of your car you can introduce quite large wind forces into the car with the backwindowsopen and driving at a fair speed and its not reallyrecommended as its been know for people to blow out the back windscreen, I thinkthat'sa load of claptrap myself but dont really knowif this could happen to be honest? Must admit I dont drive like that now just incase
Most cars generate that thump/bump sound when you open the back windows at speed as the air pressure builds up inside and gets trapped in the back of the car.
Simplest solution is to balance the air pressure in the car by opening a front window a little bit (just the tiniest gap is normally enough). I've got kids and they're forever wanting the back windows open so this solution generally works for me and without the need for any accessories.
on my last 3 cars all vitara's I fittedwind shields x4the ones that fit in the window channels by heko not the stick on typeand found they worked fine all the time you only open the windows to the depth of the shields come rain or shine no problem,if you open the window fully then it is as normal windy.