I recently got this old 1.2kW soviet made space heater of type “Луч”. The heating resistors/spirals are fine, but the fan was making loud noises. This usually indicates a bad bearing somewhere. Furthermore the heater had a unearthed East-German/Soviet type Schutzkontaktstecker compatible plug, which I was going to swap out to an earthed plug (and also a respective line cable with earth wire).
The inner workings are fairly simple: There is a thermal cutoff, then a rotary switch selects which of the heating spirals get supplied and also powers the synchronous motor. A really interesting thing is the thermal cutoff which is a Bimetallic strip but rather than using a mass produced thermal cutoff, they did one customly.
At this point of disassembly I noticed that the bearings at least on part of the motor are out of brass - so no way they would make noise. By manual rotation I found out the motor was making the noise, indicating that the rotor is rusty. So I disassembled the latter and I found it indeed to be rusty. After cleaning it up and reassembling the fan it became fairly silent.