Personally, if it was anything air related I'd be looking at the air filter.
I had a dodgy paper one many years ago that made the bike sound stuffed up, which is what prompted me towards getting a K&N.
Bit of a ballache but why not remove the air filter and start it up and see if it sounds any clearer? Wouldn't really advise taking it for a spin though, just in case you very unluckily suck something into the engine, but you're not a newbie so should hear a difference.