It happens right after the pump comes on in the morning, but stops after the water quits bubbling from the jets. It started doing this daily after my most recent backwashing.

The pump is 2 hp, the filter is Anthony "Apollo" model # VA 52-2, 52 sq ft.
Don't know if it is a multi port.

We add 15 one lb coffee cans which is what is reccommended, after backflushing.
Backflush procedure is: With pump on, hook up hose to backflush valve, then open valve till water runs clear, then close valve and repeat.
The seal on the pressure relief valve is broken so it does leak a little. I have a new one coming, so maybe that will fix the problem.