If you want to focus on something, just google it - depending on what it is you'll get Wikipedia, some blog posts, and maybe a book or two on the subject.

What Facebook / Twitter / Blogger / etc. are good for is providing context - why should I be interested in something. Generally it's as simple as "I like Mr. X and he's interested in Y". They're also reasonable at finding new topics to explore, although if you dive deep enough it turns out that everything is interconnected and you'll find it anyway.

It's really hard to define "topic" or "noise" in a way that isn't based on search keywords or (facets of) people.