Mike... I wish swamp coolers worked here! I remember them fondly from my days out west courtesy of Uncle Sam's Air Factory... I'm stuck with killer electric rates and refridgerated air due to the humidity... Not much evaporation in a steam bath!
As I recall swamp coolers are generally fed with a small dia. copper line that usually taps onto a hose bib and is strung up to the swamp cooler.
Water hammer is caused by a high velocity flow in a pipe coming to a sudden stop. This causes several occilations with poorly secured pipes banging.
That said a few cures that could help would be to increase the pipe size effectively lowering the velocity, and securing the pipe better to control the banging. Other things to do would be to not open the supply valve as much to slow the flow and also install a water hammer arrestor at the swamp cooler. Any or, all of these steps may solve your problem.