I have a 97 Explorer 4x4 with V6 SOHC
Yesterday while driving it started making a loud revving/Vacuum sound only when I am coasting/slowing down. As soon as I accelerate, the noise stops. It only happens when I am traveling at higher speeds around 55/60 mph and when let off of the gas to slow down the noise starts as it gets below 2000 rpms. It does not make this noise at idle and I can not duplicate it while revving it up in the driveway. It only happens when the vehicle is in motion. I can not tell a difference in the way that the vehicle is operating, other than hearing this noise. Any ideas?