What could be causing this buzzing sound?

See a doctor.

Tinnitus. Often caused by spasm of the Tensor Tympani muscle. All sorts of muscular and neuromuscular disorders cause muscle dysfunction in the muscles that come from branchial arch 5. Might also be a sign of noise induced hearing loss. Have you been listening to your iPod too long and too loud? Are you dizzy. Could be Meniere’s. Do you take meds? Some chemicals will do it. Call the ENT doc. Tell him I sent you.

@josie I just googled Tinnitus and it makes a lot of sense in light of my symptoms. I suppose I’ll have to suck it up and schedule an appointment with my doctor. Anyway, thanks for your answer!

I wonder how much of a discount I’ll get when my doctor hears that @josie the flutherite sent me?

It is not likely to be Meniere’s, since you do not complain of dizziness. The fact that it only occurs with louder sounds does not suggest pre-existing noise-induced hearing loss. It may be something as benign as a flake of cerumen up against your eardrum that rumbles against it with higher intensity noises. Or it could be damage to the chain of bones behind the eardrum—have you had any injuries to the ear or your head? Or there could be some rare condition with the auditory nerve, but again that seems highly unlikely considering the symptoms being so isolated and having no other related hearing or balance issues.