I don't know about any noises that the water pump makes but just follow the pulleys on the engine till you find the water pump. It is pretty obvious once you recognise which pulleys do what. The alternator has wires on it, power steering has small hoses on it, AC compressor has metal pipes coming off of it and then the last pulley is your water pump. Just relieve the tension on the belts using some of the tensioners, you probably will have to remove the radiator cause vans don't have a lot of room between the engine and front of the vehicle. Buy a manual for your van for pictures if you need them, just remove anything in the way of the water pump if there is anything. I don't think there should be much in the way though other than the belts and maybe the radiator fan. Make sure you keep track of all of the parts and where they went, take pictures with a digital camera or draw a diagram for yourself if you are unsure that you will remember. The water pump is kinda bolted into a hole on your engine and should be pretty straightforward to replace... I'd probably check your thermostat first though since you aren't sure if it is the problem. Thermostats run under five bucks usually and are pretty straightforward to replace. If you want to check to see if your old thermostat works remove it and put it in a boiling pot of water on the stove and see if it opens up when it gets hot enough and closes when it cools.
