Loud whining sound when the car is warmed up, especially on very hot days.

On very warm/hot days, after the car is warmed up, you can hear a loud whine in the rear of the car. The hotter the day, the louder the whine. Doesn't happen when first starting the car; only when it's warmed up and on hot days.
The fuel pump was replaced in January/February.
Car has approx 83,000 miles.