The truck is a crew cab and I noticed i can hear a air noise like there is a fan going in the back seat area and gets louder on highway and when you step on gas pedal .When i let off gas pedal it gets slightly quiet.
RepairPal Certified shops can diagnose and repair your 2006 GMC Sierra 1500. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
I put a rag in the vents in back of rear seat and its not as loud