LogFAQs > #976680817

That sssssss is the water filling up the bowl. It means there's a leak in the flapper(the white thing of yours at the bottom of the tank). When the water level gets to a certain point, it causes the water to kick in and fill the bowl.

If you rent, call the landlord. If you own, go to Lowes/Home Depot, and buy a $15 kit to replace all of it. The big black floater in your pic is an old style. Get a newer one installed. Toilet stuff is a very simple fix.