If you are alive, and live somewhere, then you probably have a radiator somewhere where you live right? It could be one of those big ones or one of those ones that are built into your house. Sure they keep you warm but don't you also hate them? If you pay attention, most radiators when they are on, actually make a lot of noise, whether it's light cracking or popping or whatever.

I just recently learned that it drives me crazy, lying in bed at night and then randomly hearing these purses all around my walls and floors, sometimes even thinking that it's a rat or something, and it always bothers me.

Does your radiators/heaters make noise too? Do they distract you?

I use my space heater so rarely - I'm always too hot - that when I use it the noise doesn't bother me at all.

Does the noise come from a centralized heating system of a portable one? If it's the former then it's probably an old system (central gas tank heating water that then travels through the house) that would require maintenance. Otherwise most modern portable heating devices are even quieter than air conditioning units.

Like janus, me and the rest of my family barely ever use our portable space heaters. Our furnace is very successful with keeping our house warm enough for all of us.  However, earlier this winter our furnace went out so our house was very cold. We had to use our space heaters to keep warm. Plus I really didn't feel like wearing a winter coat indoors XD

Our portable space heaters are always making noise but it's actually a pretty quiet and relaxing noise. It doesn't distract me unless it turns off often. Sometimes it does that once the temperature it's giving off is at its highest. My parents told me that's supposed to happen so I'm not concerned about it.

Hm… Nope. I've never had the issues you described with any radiators/heaters that I've come across whenever I actually have to use one, and I don't hate stuff that brings one warmth.  Then again, sound doesn't bother me all that much unless someone's doing something like holding a earsplitting concert next door in the middle of the night when it's not a holiday, and even then, if it's something the police can take care of easily, I don't tend to worry too much about it either. I also don't have any problems with rats or bugs or whatever (my pest control actually works), so I don't even consider those possibilities when I hear strange noises. In fact, odd sounds that I hear more often usually turn out to be/are more likely to be bears, birds, boars, raccoons, deer, bunnies and other similar animals instead. All in all, my radiators/heaters don't tend to "distract" me in any way.