do like my kids use to do, turn up the music..
at least checking replacing the fuel pump would not cost much,
neither with the water pump, if one or the other does not fix the problem you will still have them for later on... and later on would come sooner or later.. I have never heard either one rattle but........the only thing that I heard close to that was in a 55 chevy, I thought the thing was going to come apart, turned out to be one lose bolt in my fly wheel cover that was moving around..
let us know what you find out