Hi, I just got new sprinkler valves put in (Rainbird ASVF anti-siphon ones). Every time a valve shuts off, it makes a loud squeak, like plastic rubbing or deflating balloon (not water hammering). It happens on every valve, and my old valves did not do this. Is this normal? What could be the problem? This is very annoying because the sound is carried through the pipes and is very loud inside the house. I plan to call the installer about it on Monday, but like to have some background knowledge first in case he tells me, "that's just the way it is." Thanks so much.