Floor squeaks are usually where the sub floor and floor joist meet. If there is a space between the sub floor and the floor joist and it is not properly glued and fastened, you get a squeak.
Also, sometimes where the bottom wall plate and the sub floor meet -- for the same reasons -- you get a squeak.
It should not make any difference if you add a felt paper under the Aluma-Foil. Make sure you are stapling the hardwoods with a 2" staple to insure a secure floor. The staples should be nailed in through the tongue of the plank at an angle so that the staple is hidden when the next plank is put in place. The only areas that will have to be face-nailed with brads will be right next to the wall.