I have a 1995 F250 4X4 and when I turn the engine on, as it warms up, it sounds like someone is pouring a pitcher of water behind the dash board. No leaks and the heater works fine. After a while it goes away as it warms up. Any ideas?

 

Just taking a guess here... Sounds like you have air in your system. What I mean, is the radiator level all the way up.

 

If you do have air trapped in the cooling system you can do a search on GOOGLE, "trapped air in the cooling system" and several sites will come up that suggest methods of getting the air out. They are not very complicated.