I was thinking about it and my assumption is that my coolant is low. This would cause the water pump to spin faster and pressure to be decreased allowing me to here the water moving through the water hose.
it is the water flowing through the heater core. when you speed up you hear the water rushing sound, sounds like its comin from the passenger side floorboard right? what year truck do you have? what you need to do is to bleed the air out of the cooling system, you are either low on coolant or have alot of air trapped in the system, so fill it up and bleed it, and the sound should stop. hope this helps!