2002 Buick Rendezvous Wining Noise

I have a winning noise that is coming from the engine. The noise comes from the engine, when you start the car the noise is there. And when the car gets warmed up the noise is not as loud, but when you apply gas the noise gets louder as you apply gas and when you let of the gas peddle the noise goes away. For example when I'm on the highway or driving the noise only comes when the car is accelerating and when I'm not stepping on the gas the noise goes away. I have replaced the power steering pump and the water pump. After that the winning noise is still there. I used a stethoscope to listen to where the noise is coming from, and the noise is coming from the water pump when I'm listening and applying gas. I have noticed that the manufacturing has changed the design on the water pump for the Buick Rendezvous 3.4L. I don't know if that has anything to do with it. Please help me find out what I am doing wrong? I think that maybe the new water pump is bad. Also another thing is after flushing my radiator and the new water pump in, I only put in maybe about almost a gallon of coolant in the car. I even bled out the air bubbles out of the coolant lines, and I have heat in the car.