Vortech noticable whistle at idle. Sound disapears at WOT.
KB no sound at idle. Whine/turbine/747 sound gets louder the higher the RPM in WOT... Minor sound of the bypass in partial throttle. Have to pay close atttention to notice.
Centrifugel Blowers are generally loud at idle, and get quick when you romp on it. My vortech V1 sounded like 1,000 angry crickets singing in unison at idle and low rpm chugging.
Roots and Twin Screw blowers are silent at idle and partial throttle cruising, and scream at WOT. They sound like a 70's police siren, I love it. The Twin Screw from Kenne Bell sounds like an Eaton Roots, except louder and higher pitched.