As a Realtor for over 20 years in Calgary, I've experienced so many unique situations and watched other professionals fix small problems enough times that sometimes - ok, more than sometimes - I get called upon by my friends & clients for non real estate advice. I'm far from being a plumber but this "hissing" sound was something I had seen many times on Toto toilets.
Calgary has notoriously "hard" water and its high mineral and chlorine content will eventually eat away at the rubber inside the toilet fill valve assembly. I had previously helped a friend install a Korky replacement fill valve but noticed afterwards there is a replaceable rubber valve available if you're willing to take the assembly apart. I tried it out myself and was able to do the whole repair in only a few minutes - while one hand held the phone to record a short video!
The neatest part is that I uploaded the video as a bit of a joke ("Plumbing with Jeff!") and it quickly gathered more than 2,500 views and became my most watched video by a very large amount.
If you're looking to chat about Calgary real estate, give me a call/text! I'm easy to reach. Looking for a plumber? I'm not your guy - but I'm happy to recommend a professional that will be able to help you out.