p0440 and rattling from the front

[xtrememeasures]

I constantly get this p0440 code coming on with my truck. I scanned it and looked it up on here along with searching. I saw some reasons for this but they looked more like guesses. I have a bad fuel pump...the good ol can start if the tank is 1/4 full or below so im assuming this might have to do with this code also as some alluded to the fuel pump gasket. what are your experiences if any with this problem?

Also at startup i get this rattle from the front. came out of nowhere! it will become more apareant at low rpm then go away when gas is given. actually no that i think it happened after i changed my alty. when i go into revers it will go away then while i shift into d u hear it rattle and it almost feels like the truck hesitates for the smallest amount of time then the rattle goes away once i give it gas....or i think it does as my exhaust might be hiding it. what are your experiences with this also?

thanks!