When I press on the gas on my 2002 Mercury Sable I hear a squealing noise under the hood. What could that be?

Most likely the fuel pump is ok, but there is likely air in the fuel line that you need to bleed off under the hood.

It is possible that the fuel pump went bad, and the way to know is to check the fuel pressure (same place you bleed it under the hood). The fuel pump is in the tank, so it's a real pain to change.

Check for bad window door motor inside door panel

check either for wheel bearing or worn tire,uneven surface.

it should be located under the dash to the left of the steering wheel or in the power box under the hood

under the hood, in the firewall the clip at the motor became disconnected to the rods that move your wipres -- there's a way in there,. you will have to look and maybe remove some facing materiasl which cover the access holes... the clip is most likely in there somewhere too -- you will have to look real close and you will find it...

Best regards
Ck

THE PROBLEM IS THE DASH LIGHT DIMMER CONTROL IS EITHER TURNED OFF OR THE DIMMER IS DEFECTIVE, HAVE SEEN BOTH. THE DIMMER IS NEXT TO THE HEADLIGHT SWITCH

...are under hood, a diagram on top of radiator support.

you should have one under the hood

There are also two serpentine belt types for the 2002 sable. The S and U type engine. Take the old belt with you the the parts store. As for the diagram, I googled it under images and about a dozen correct ones came up. Remember the 2002 sable is the same as the 2002 Tarus.