Typically a thumping noise from your hot water heater is an indication of sediment build up in the bottom. It results in uneven heating and you get the resultant thunk, thump and groan sounds. At this point you should do a drain down and flush to get what you can out of it. Turn off the hot water heater if it is gas or electric. Hook up a hose to the drain cock near the bottom of the heater and run it out to the sidewalk or driveway so that the hot water does not kill the grass. Turn off the water supply valve to the heater and then turn the drain valve fully open. This will start draining the tank. Depending upon the size of your tank this will take a while. After it has drained, turn the water supply valve back on to the water heater and leave the drain valve open and allow it to flush until you have no more sediment coming out of the end of the hose. It helps if you have a dark surface that the hose is draining on to see what you are getting out. Allow this to run. It may take 15 to 20 minutes. Then shut off the drain valve, disconnect the hose and allow the tank to refill completely. Turn the hot water heater back on, be it gas or electric, and you will have done what you can for your heater. It is suggested that you do this multiple times a year to keep your tank clear of sediment build up. If your heater is electric, you can remove the element at the bottom and try to suck out some of the gunk with a wet vac with a small pipe attached to the wet vac hose. Make sure the element is turned off before draining and removing. Make sure the tank is full before starting it back up with electric to prevent burning the element up. Good luck. If this has proven helpful, please remember to hit ACCEPT, otherwise I do not receive credit. Thank you.