I saw this thread and it seems like the consensus was either the check valve or valve actuator.
http://www.poolspaforum.com/forum/index.php?showtopic=9637
We just moved into the house and this started happening. We replaced the check valve but it still happening. And I don't see anything that looks like a valve actuator on my equipment? (NOTE: First time home buyer, first time pool owner)
Here are some pictures of my equipment.
Any help would be greatly appreciated!!! and yes, we are going to be replacing the spa filter container since it looks like CRAP! =)