I had the dreaded steering wheel buzzing noise and read through all of the threads on this topic. Seemed like the likely culprit was the airbag. I didn't want to take out the airbag completely so I just took a T-30 torx screwdriver and loosend and tightened the two screws on the side of the steering wheel. This allowed the airbag to slightly adjust back into the steering wheel. No more buzzing.

Pretty much what I did on my 05. It took a bit of finessing but it's been gone for years now.