I get the feeling this varies greatly from person to person. e.g. If I'm in a coffee shop I pick up fragments of conversation and can't help but try & isolate specific voices. I've tried - I can't block it out. Fragments of conversation to me aren't noise...they're fragmented info requiring more brain power to decipher.

This might just be me though - I think in German, read in English and hear Afrikaans in coffee shops. So I'm all kinds of messed up anyway when it comes to spoken language.