...after filling up the gas tank, I hear a metallic rattle when accelerating, around 1800 rpm. It does go away after the first 1/2 gallon is gone.
I haven't checked underneath yet (I don't have a properly-equipped garage ), but I'm pretty sure the weight of the full tank causes some unwanted contact with the exhaust or some part that holds it in place.
Is there a way to lower the exhaust (maybe 1/2 ")?