2004 Chevy Impala Strange noise when accelerating

Yes it could be your water pump. If your water pump is leaking, some coolant will get on the serpentine belt and make it squeal when your engine is on.
Check your pump for leakage and replace it right away if it's bad. Don't keep driving the car if it's low on coolant because it will result in very expensive damage to the engine.

Another possibility is that one of the pulleys driven by your serpentine belt is slightly crooked which makes the belt rubs on the sides of the pulley resulting in squealing. Also, it's possible that your belt is loose on the pulley (either it's stretched or the belt tensioner is no good anymore). It's also possible that one of the components driven by the belt is on its last leg (which includes, as you mentioned, the steering pump). Does it make noise when you turn left or right? Have you checked the steering fluid level? Any leaks, either at the pump, or under the car at the pinion rack, boots, etc?

Hello fellow Tennessean (Clarksville here),

Here is a little tip to troubleshoot a belt noise problem:
Using a spray bottle filled with water, mist the belt lightly. If the noise level recedes for several seconds, then returns louder, a misalignment problem is likely. If the noise immediately increases after the belt is sprayed, slipping is likely.

Hello there and thanks for the feedback.
I'm " œglad' to see that a bad tensioner was one of my suggestions... People usually leave no feedback so I can't tell if I've been able to help or not.
If you haven't gotten the tensioner replaced already, it's an easy job. You can do it yourself and save you some money. I replaced the tensioner on my wife's 03 Impala last year, and it took about 10 minutes (because I'm slow). The part itself is about $40 if I remember correctly.
Anyhow, I'm glad you found what was wrong. Enjoy your quiet car now :)