guys, one more thing.. it isn't a problem, it's more like a thought that hasn't found an answer

when i set the trust to idle in the A310, the master caution springs to life and the memo display shows me "Hydraulics" and "Flight Controls" for a moment, and then it returns to normal and the caution warning disappaers again..
why is that ? can someone shed some light on me and help me understand, 'cause my thinking hasn't given me an answer :%
