If your icemaker is turned on but your RF26X is either not connected to a water supply or the water cannot make it to the icemaker due to a clogged filter or obstructed supply line, this noise is not unusual. If the refrigerator is not connected to water, turning the icemaker off should eliminate this noise. If the water is connected but the icemaker is knocking and not producing ice, check the water valve and lines, make sure that the refrigerator is not too cold which can cause the water lines to freeze, and check the filter to make sure it isn't clogged.
If these suggestions do not help to explain the knocking noise, I would suggest you visit the Troubleshooting Guide through the link below, then select "Troubleshooting ► Noise/Vibration" for additional explanations and troubleshooting suggestions: http://support-us.samsung.com/cyber...
answered 1 year, 7 months ago