Are they hungry? No. Wait. Healthy chickens are ALWAYS hungry! You can try tossing some scratch around the run to give them some busy-work. The other thing is to look around really hard for something "scary," which would cause them to squawk until you appear. For example, here are a few oddball things that have terrified my (or my neighbors') chickens over the years:
Sudden movements of pretty much anything within eyesight
Anything flying overhead - hawks, low planes, kites, trash, a Frisbee
The neighbor's cat sitting 20 feet away
An overgrown fox grape vine casting shadows as it swayed
Moving headlights
Christmas lights along a fence (looked like eyes at night ... they calmed when we took them down)
A small Super Bowl pennant
A beach ball
Clothes on the line - especially sheets
A treat can left where they could see it but not reach it ... frequently!
A loose gate swinging in the breeze
A blowing curtain hanging out a window on a beautiful Spring day
Some of this stuff was really weird and hard to figure out (like the Christmas lights!) We needed to think like a chicken and remember that pretty much everything is scary to a critter who's only one step above grass on the food chain!
Good Luck!