The humming or ticking noise if often caused by a vibrating boiler. This can have several causes.
For example in summer, it’s common for people to shut down all radiators. If the weather-dependent regulation is asking for heat production, the boiler can’t release the pressure. You can test this by opening (a) radiator knob(s). If the humming stops, you’ve found the problem.
In this type of systems of an adjustable bypass is mounted. Turning this bypass more open can be a solution.