hello ford fans,

my truck has 88k on it, automatic trans. just picked it up 3wks ago, it starts, runs, pulls nicely.
it has a strange knock, not like mechanical almost like fuel but possibly only one cylinder at 40mph w/overdrive on up to 60 maybe higher. also only at cruise/lite throttle mainly. if you step on it a little like you're going up a hill and just want to keep your fixed speed up it may get louder, not sure. if you step on it about half throttle all you hear is turbo and torque, knock goes away

Thanks for any advise.