Noisy mechanical room

residents were asked to test the water heater and boiler because believe that it is very noisy. I replied that I had no such equipment.
but are there any rules to the noise level of the boiler? water heater?

Unusual noise from any mechanical system could be cause for concern.

You could routinely inspect the water heater and boiler to determine if they are operating normally, installed correctly, etc.

Perhaps the noise is an indication of a condition or problem, or perhaps its normal noise.

Dom.

What kind of noise? Who are the residents? What kind of building? what equipment? You are an engineer?