Cockpit Noise Level B787
The noise is mainly from the air conditioning air flow. Compared to every other Boeing I’ve flown it’s very quiet. Normal conversation level is easily heard.
Having been on quite a few different flight decks over the years, in reasonably modern ones the majority of the noise appears to come from the air supply, unless you’re in the upper reaches of the speed envelope. On airtests when you shut down all the packs to see if the cabin rate is acceptable, it’s unnervingly quiet!