After checking that the drain line and the pad looked fine, I noticed that the rubber tube that carries the water from the solenoid to the top of the filter pad wasn't quite seated to the bottom of the nipple.
I turned it back on and noticed that when it first starts, the rubber tube slips up a bit. I figure that the calcium in our water is probably building up in the tube causing a little more pressure when it starts up. So I just put a zip tie on it and will monitor it going forward. At some point I will need to soak it in CLR :)
