I posted earlier that a whistling sound occured when I installed a 75 mm Accufab throttle body and 75 Dragon plenum. I thought that the sound was coming from the tb but it has turned out to be from the plenum. When I complained to Dragon Performance Parts, they responded with an e-mail acknowledging that the whistling was common and that it was caused by the divider in the lower plenum. If you don't want an annoying sound coming from your engine, you may want to purchase an Accufab or C & L plenum.