Sounds as if the controller took a surge and is putting out power to one or more stations simultaneously. Check the output of the different zones by testing the output at the controller with a volt/ohm meter. If that is the case, the controller will need to be replaced.

All Wet
Texas Licensed Irrigator #1897 since 1984

I had a similar problem and the contractor told me that in order for the valves to close there needs to be adequate water pressure.... I was running my well too low and having almost no pressure and then the valve wouldn't shut.

Para,
True, valves close faster with higher water pressure. Anu, does the valve shut off when the controller is unplugged? If so, that also is a telltale sign that the controller is malfunctioning. We replaced a controller just today that was exibiting the same symptoms due to a lightning strike. Remedy: Replace the controller or if you have extra stations on the controller, move the wire from the guilty station to another station at the controller.

All Wet
Texas Licensed Irrigator #1897 since 1984

Recent lightning strike victim reporting in. Zone would not shut off. Followed All Wet's advice and rewired offending zone to an empty zone. Worked like a charm. Thanks All Wet.

I too have been fighting this issue. I had the pressure regulator for the house replaced, all the sprinkler valves and unplugged the controller and it's still chattering. Now the city is coming to check the pressure from the street, is the only thing left to do put a regulator on the sprinklers?
Any answers appreciated thanks