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There are 2 possible cause for noise similar to what you describe (nose descriptions are very subjective). One is from the expansion that occurs when a cold heating pipe heats up. If the pipe is binding against a framing member along its run then that will create noise but I'd describe it more as a ticking noise. Not much you can do about this if the restriction/binding is in a concealed spot in a wall or floor. The other possibility is air i the piping combined with water that's a bit too hot in the system. If too hot water meets a pocket of air it can flash to steam causing a banging (or knocking) noise. The noise can range from insignificant to extreme depending on water temp. So you could try purging the zone that includes the problem room if you have copper baseboard. I can give you instructions but they are pretty involved.
The piping may be free floating inside the room but does it pass through any walls (or floors) to get into the room? The fact that your description emphasizes noise only in 1 room those are the only likely causes. If it was some noise at the boiler, like from debris in a pump, then you're probably going to hear it in more than just 1 room. I'd still consider purging the system.