Probably when the element switches on to heat the water. Can't tell you what parts you need to replace without seeing & testing it. Could be the element, wiring, thermostat etc. You need to have the test meter & knowledge of where to check & how to test to fix a fault like this. If you don't have either then save yourself a lot of time & money by getting someone in to do it for you.
Lincoln Appliance NZ, May 2009
