I have a 2001 Chevy Impala 3.8L with 92k on it.

It recently started making a "screeching" or "whining" sound while driving.
When I'm driving the car and let my foot off the gas, it will make the sound for about 3-5 seconds. If the sound begins and I hit the gas, the sound disappears. The sound usually only comes after taking my foot off the gas pedal.

Anyone know what this could be? Thanks.

A vacuum leak somewhere? -- in general, manifold vacuum increases as throttle position decreases.

Intake Air box not closed correctly? -- also check the intake tubing around the throttle body.

The power steering pump makes a whining noise, especially when the fluid is low or cold -- it is behind the glovebox in relation to the driver's seat.

Where does the sound appear to come from? -- be as specific as you can.