When I shut one of the windows in the front room, this is what I heard:
The snap was the rope in the window sash breaking.
The clunk was the counterweight dropping to the bottom of the window.
I may or may not have cried a little.
In theory, I know how to fix it. I'll have to pry off a piece of trim on either side of the window, take the window out, pry off the little piece of trim that hides the rope and pulley system, pull out the broken rope, string a new rope through the weight, and put everything back like it was. I've seen other people fix windows this way, but I have never done it. Hence, I know how it's done in theory but not in practice.
I'll add this to the to-do list. Sigh.