Of all the jobs you could bring to a bike shop, this may be the one you want to the least. If you're lucky you'll find a good mechanic with incite (or just plain luck) who'll find the problem in short order. More likely it'll involve lots of time, wasted effort, wasted replacement of perfectly good parts, and a pretty expensive tab, and no guaranty of success.

Try to work through and eliminate anything you can and only see the dealer after clearing the field.

To give you an idea of how difficult this can be, here's the causes of "bottom bracket creak" on my commuter over the years. Saddle rails twice, pedal threads 4 or more times, broken rear axle, loose toe clip screw (god that one was a pain), stem creak (could of sworn it came from the BB area), loose chainring bolt, and a few other things that resolved on their own so I never found them. It never was a loose crank arm, nor anything related to the BB.

My all time favorite was a newly installed front derailleur cable that I trimmed a bit long, touching the left crank arm.