If you have a zone on, can hear water running in the system, (from the backflow or valves, etc) but don't see any heads popping up... you mentioned a wet spot on the lawn... I'd consider looking into a possible break in the pipe in that wet spot. The broken pipe will take pressure away from that zone popping up or perhaps prevent it from running all togehter If there is no leak, consider a valve problem.
Mark Cardarelli
RI Master Irrigator #000003
Ocean State Lawn Sprinkler, Inc.