FAQ Search Select a Category BarkBath Cleaning Formulas Cleaning Tips Commercial Products Corporate Deep Cleaners Hard Floor Cleaners Mops, Brooms and Brushes Parts and Accessories Steam Sweepers Vacuums Warranty Web Site and/or go My Steam Ready™ is Making a Knocking Sound. Why? Answer: Is this the first use of your machine? If it is NOT your first use; then water is not able to get into the machine. Is the water tank full? It should be. Check to see if the water tank is seated properly in the machine with no gaps. You will hear it "click" into place once it is seated properly. Ensure the cap and insert assembly is screwed on straight to the water bottle. If it is not, the tank will not sit correctly in the machine and will not release steam. See pictures below for correct/incorrect: Has the machine sat not used for a long period of time? If so, plug the machine in and hold the trigger for up to 1 1/2 minutes. This should stop the knocking and the machine should start steaming. However, if the machine is in use and continues to make a soft knocking sound, this is normal. If this is the very first time using your machine; hold the trigger down until the noise goes away for up to 1 1/2 minutes. This is the normal sound of the pump trying to pull water through the machine. It will happen on the 1st use, each time the unit runs out of water, and if it sits for an extended period of time allowing the water to evaporate. Please not that while in use, the pump will continue to make a soft knocking sound. This is normal. If this knocking noise lasts much longer than the first 1 1/2 minutes of use, or is a lot louder than a "soft knocking noise," please contact us at this link for further assistance: http://www.bissell.com/support/contact-us Related Questions How do I use my Steam Mop to sanitize my floor? My Steam Shot™ is spraying water only or steam and water. What should I do? Why doesn't my machine heat up? The mop pads will not stay on my Lift-Off ® Steam Mop foot. What can I do?