[Kodiak]

I live at the top of a 2 mile climb, steep enough to keep the EGT at 500 under 15psi of boost. Sometimes, when I get out of the truck I can hear a soft whistling from amidships, underneath. It's worse when just filled up, and the sound quits immediately when I open the fuel cap.

I replaced the fuel lines last winter. Any ideas what it could be?

Thanks.