All of the flex lines we provide are whistle free. In order for a large volume of fuel to continue through the key valve on to the burner without any loud whistling, a special line is required. Some standard, yellow flex lines will whistle very loudly when you turn up the fire.
Keep in mind, there’s a difference between whistling and the sound of mild, rushing wind. No matter what, you’ll probably have the sound of air moving through lines. That’s normal. Sometimes if there is moisture in the line, it can cause a mild whistle or gurgling sound. Over time, it should evaporate. Meanwhile, keep the burner covered when it rains.