2nd Gen Non-Engine/Transmission Unknown clicking/buzzing from frontend...any ideas?

[BJonesUSA]

Ok, I've had this annoying clicking/buzzing sound coming from under the hood for about 3 years now, but can't pin down what it is. Sounds like a playing card stuck in a bicycle wheel. It only occurs at 30mph or faster, isn't engine or brake related, but increases in frequency with increased airflow (either headwind or faster speed)... Didn't know if anyone else has had this occur, but I'd really like to figure out what it is so I can ride with the windows down and enjoy the sound of my Cummins purring!