Whistling Trumpet 5702-image-1The ability to change the sound of a blow-off valve is increasingly becoming an important issue with buyers, who want to sound different from everyone else. In 2004, the Whistling Trumpet was released which emitted a piercing screech when driving aggressively. The 5701 can be used in place of the standard trumpet on GFB valves (Part numbers T9003 & T9503), and will make a whistling sound. However, it is necessary to run the valve so that all (or most) of the air vents through the trumpet à Respons valves will typically not generate the velocity required to whistle when set to 50/50 venting.