I have a f250 7.3 2000 and only when it is real cold after I give the truck over 10 minutes to warm up it makes a loud air rush sound from under the hood near the air vents while I drive. This happens only when I'm driving and when I'm cruising. If I hit the petal it will stop for temporary until I cruise at 1 speed again. When this air rush sound happens I feel a significant decrease in power. When it gets warmer outside this will never happen.