I have a gas fired house heater water circulating making bump sound occasionally. We have never heard it before this few days. When I heard it, I went and listened and it was not during firing, but possibly right after or at shutoff, because everything was very warm. Should I be concerned? Any preventative maintenance to do? Thank

It happened again, after the heat cycle. I thought it came from the ceiling where the heat vent or else pipes were contracting after the cycle.

Actually every heating system especially boilers should be checked every year. The noise you here could be coming from the pump on shut down or a bit of air might be in the system. Noises are almost impossible to detect here but are better checked in person by a visit from your local HVAC person. A slight noise lie that is probably nothing to worry about BUT it might be smart to get it checked.