1, when there is scale in the boiler heat exchanger, when the temperature rises above 65 degrees, there will be rumbling in the heat exchanger. In severe cases, there will be a slight shaking feeling when touching the boiler shell, and scale cleaning is needed. This often happens when the boiler needs frequent water replenishment and uses heat sinks. According to your description, it is not such a problem.

2. There is a lot of dust on the fan blades inside the boiler, and there will be a lot of noise during operation, similar to the noise of automobile engines. In severe cases, the boiler will shake violently. According to your description, the sound doesn't sound like this question.

3. When the boiler is just ignited, the radiator squeaks, which is similar to the sound of folding corrugated iron sheets. This is because the fins of the heat exchanger are deformed due to metal expansion caused by local heating. It will disappear after one minute of ignition, and it will appear again after the boiler has just stopped running. This kind of sound is very common and does not need any processing. According to the voice you described, it is probably this reason.