i noticed one of the sprinkler heads leaking when the water is off.
the system still waters fine but that head seeps when everything is
off. i thought i just needed to replace the one head so i removed and
capped it. when i capped it the other two heads in the zone started
seeping(more of a fast leak...spray up a little). the leak seems to
come and go...if i turn if off and on a few times it may stop leaking
but only start up again next time its used or what not. the sprinkler
system was self-installed by the previous owner and i don't know where
anything is under the ground. what could it be?

thx