95 year old thinks the furnace & radon fan from the apartment below her are so loud she can't sleep or even think - we can barely hear it. What can be causing this?

First she only thought the noise was bad in her bedroom, now the noise is different rooms. We can hear the fan and furnace if we stop and listen for them but she insists they are VERY loud and that she can't watch TV or sleep because they are SO loud. Sometimes the noise stops or at least gets quieter but then it comes back very loud and stays constantly loud for days. We have spent time with her listening for the noise but we never think it is loud enough that it should be bothering her. She is a little hard of hearing and turns the TV way up when she watches so I don't really think there is any way she could hear the noises with the TV on but she insists she can. She also has macular degeneration & I know that causes visual hallucinations in some people but she has not experienced those. In all other aspects of her life she is doing well, she still does her own cooking and laundry and most of the cleaning. She has a dog she takes care of and takes for walks. But with the noise she hears she is not sleeping and she is becoming very depressed. What can be causing this? What can we do?