I noticed something hanging off my truck underneath. The rear strap for the gas tank was broken. The tank was 3/4 full. Luckily the ford dealer parts dept was open on saturday and had the parts. I bought the front and rear straps. Replaced the rear right away, will do the front later. Thats probably where the clunking noise I've been hearing has come from. No more clunking sound.
They are easy to replace. Except rusted bolt. My brother helped. Support the tank with a jack, remove bolt, hook other end in slot rebolt. Took about 20 min. I need to do the front still. I think both straps cost around $60, Thats from ford.