My mom is listening some buz sounds.

From some days my mom is saying she is listening a buzz sounds while sleeping at nights ( like a mosquito or an insect sounds) She is saying some insects are making noise and telling me to see,but I can't see anything and I am not getting any sounds. She is saying suddenly some sounds (like ssssssss sound )are coming and again it is getting back normal. What is happening doctor ? From some days I am observing, first day when she told like this, I searched full room and told nothing was there, but after that also she is complaining some bugs or insects are there, they are making noises, I am side of her, but i dont listen any thing. What is happening I am not able to understand. Please help me doctor what to do and what Is the problem