The electronic valves in a sprinker system close fast. The shock in the plumbing system resulting from the sudden stop of flow is called water hammer. This water hammer is damaging to pipes and fixtures, so you should fix it.

Air chambers, a water hammer arrestor or even a pressure tank can completely eliminate this impact. Both an air chamber or water hammer arrestor look like a vertical pipe rising from a T in the inlet to the sprinkler valve train. The vertical pipe is an air trap, and air is compressible, so when the flow stops suddenly, the air acts as a shock absorber eliminating the thunder.

Do a search on plumbing air chamber, or water hammer to see illustrations. On the first link select irrigation water arrestor sizing and you will see a digram of how to set this up. The other links are general information.

http://www.zurn.com/pages/catalog.asp?ProductGroupID=93&ProductName=Model+1250AA#p2605

http://www.naturalhandyman.com/iip/infplumb/infwatham.shtm

http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,71502,00.html