Strange noise when braking

My '99 Taurus makes a strange noise while applying the brake hard and also the brakes are very spongy when it does this.
the noise sound like it is coming form under the dash on the driversside

Is the vehicle equipped with ABS? If so, it is probably the ABS engaging.

If you do lots of "hard braking" you will probably soon develop a case of warped rotors.

The noise just started recently and it sounds like a whine or whistle.
sometimes when the noise happens the peddle goes all the way to the floor and i have to pump and push hard to stop

Leaking master cylinder into the brake booster? Bad brake booster? Are you losing brake fluid? Do you have a Midas or similar brake shop nearby that can inspect your brakes? Midas will do it for free.