Ive fitted 18'' alloys on my vw passat with 225/40/18 tyres
 

Ive fitted 18'' alloys on my vw passat with 225/40/18 tyres and ive got a sound like wind blowing or something? all ive fited some 18'' alloys on my 2006 passat and ive got a sound when driving.not shaking or anything,the sound its like a whizing or roaring.the tyres size is 225/40/18.someone told that tyres should be 235 wide.can someone tel me if i should change tyres or its somethig minor.