This incident took place when I was in my school hostel as I was a SEE student. SEE is a very important part of every teenager's school life as it determines which subject are we going to take in +2.
In the school where I was studying a senior jumped from the school building when I was in Ukg. From then most people consider that building very haunted. There were many stories which were going around during that time.
I never thought in my entire life I would have an experience like this until one day me and my friend (when ever we talk we always talk about what happened on that day) both experience it for your context. Now, I will just go straight to the point.
Actually, we were only allowed to take a bath only 2 times a week in our hostel; on Tuesday and on Saturday. During those days all the bathrooms used to be pack as there were only 4 bathrooms (2 For girls and 2 for boys). There were so many students in our hostel. It was on that faithful night when me and my friend decided to wash our hair. We only had 2 hours break and the girls bathroom was packed so we both decided we will go to boys bathroom as it was empty. On that building there were only 4 people including us; 2 of our friends were in girls bathroom showering. After we took shower we were going upstairs then we suddenly heard someone rubbing their hair loudly when me and my friend were just talking and our 2 friends were showering. After hearing that sound we just left our belongings and ran way. We were so scared our legs were shaking. We told our friends and they were in shock. After than we never dared to go to that building because of our experience.
Sorry! For grammatical error as English is not my first language.
Ever since I read your story, I have been thinking about the "rubbing their hair with a towel loudly" sound and now I wonder if this was the sound of static.
If so, it is common to report this kind of sound during a paranormal encounter, oftentimes accompanied with drop in the temperature and an overall feeling of uneasiness and being watched.
Do you remember experiencing any or all of the above when you're on the stairs that day?
The following link shows a variety of static sounds, perhaps one of them is similar to the noise you heard that day.
Https://mixkit.co/free-sound-effects/static/
Then, I guess, it's possible that an spirit was trying to manifest to you and your friend.
Awaiting for your feedback and, once again, thanks for sharing.