When a baseboard heater goes from being completely cold to hot in a short amount of time, noise will occur as the copper pipe that runs through the element expands, causing the metal fins on the pipe to make noise as they rub against each other. The fins may also make noise if the guide that runs between the fins and the place where the element rests on the baseboard track is missing; if the guide is not there, the fins will rub against the baseboard as they expand. Both of these situations generally result in a “pinging” sound.
Remove the cover of the electrical baseboard heater and gently straighten the fins using a pair of pliers. If any of the fins are touching parts of the baseboard, insert wax paper, grommets (flexible loops that offer support or reinforcement) or plastic shields between the heating element and the baseboard track. This procedure will ensure that the fins of the heating element do not rub against the baseboard when the element expands with heat.
Manual thermostats, which are set by hand to a desired temperature, often result in extreme fluctuations in room temperatures. This happens because the thermostat turns off once the desired room temperature is reached, and the heating element also turns off and cools until the thermostat turns on again. This results in an increased incidence of heating element expansion. An electronic thermostat decreases the swing in room temperature from hot to cool and back again by checking the room temperature frequently and adjusting whether the heating element is on or off accordingly. This design helps maintain the room temperature so it does not get too cold or hot. The result is the elimination of expansion and contraction in the heating element.
In some cases, buffering the fins or switching to an electric thermostat may not stop the noise. Low-quality electric baseboard heater models may continue to be noisy. The best thing to do in this situation is to replace the entire unit. In general, you should purchase a unit that will supply at least 10 watts for every square foot of floor space; if you live in an area that has a cold climate or if the ceiling height is above 8 feet, get a unit that will supply at least 15 watts per square foot. The U.S Department of Energy suggests looking for labels from Underwriter's Laboratories (UL) and the National Electrical Manufacturer's Association (NEMA) and comparing warranties among models when shopping.