I get a high pitch sound, when the dash air is on ---(only when my wife) re-directs the vent. If the vent is almost closed on the dash, it will whistle.
Do you heve the Dash A/C on when you hear the loud sound??, If so, check the Vents in the Dash--just move them a little and the sound may disappear
04 SeaBreese LX 8341 / Workhorse W-22 / GM 8.1 / Allison 5 Speed / Brazel's ULTRAPOWER Upgrade/Taylor Extreme Service PlusCables/DIYCAI
06 Honda CRV4/SE/all wheel drive with Falcon II / Roadmaster 9000 Braking System