Knocking sound when car is turned on ?

Since no one has come up with an idea, I'll answer my own question: A local mechanic listened to the knocking; said it was a 'relay' and that it was harmless. I should be able to drive without concern.... (?).

My '05 pontiac grand prix has a knocking sound that starts and stops at will even when no one's in the car and it's just sitting still. A mechanic sad it's the actuator...does anyone else have this problem?