The lower drawer freezer icemaker in my Frigidaire side by side refridgerator unit makes a very loud knocking sound every time ice cubes are dispensed. The unit produces a good volume of ice cubes, but even when a handful of cubes are removed, the knocking sound is so loud, can be heard throughout the house
My Frigidaire ice maker also started making a knocking noise every few seconds. The bin was completely full. Emptied the bin but still knocking. My wife found a post about the ice maker fan stuck on ice or frost. The knock was the can trying to start up. Pulled the ice tray and blew a hair dryer in there for a minute. The knock stopped!
With the lack of complete info, we can only guess. My guess is that the mechanism that ejects the ice into the tray when ready is failing. These typically have a little electric motor driving some gears and cams, often made of nylon or other cold resistant plastic. There is a large driving gear being driven by a small (pinion) gear attached to the motor and if the teeth on either one start to wear down, they slip on each other, making a loud clicking or banging sound. Bottom line, it is about to fail completely, you need to replace it. Some can be repaired, some cannot and you replace the entire ice maker. http://www.acmehowto.com/howto/appliance/icemaker/repair/ejectorgear.php