Ringing in the ears (which some people experience as a kind of buzzing or high frequency whine) can definitely be caused by mercury exposure. My thought is that when your amalgams were removed, perhaps you were exposed to large amounts of mercury vapor (especially if you didn't have your own oxygen or if the dentist didn't use a HEPA-type vacuum during the drilling procedure). Even with all the safety precautions in place, it seems only reasonable that there would be at least some minimal mercury vapor exposure.

Plus, once all the amalgams are removed, according to Hal Huggins, you body starts releasing some of the "stored" mercury in your tissues, which makes its way into the bloodstream for removal from the body via the liver and colon. Some of the mercury can very easily get re-absorbed back into the blood circulation to be re-deposited in various fatty tissues such as the brain. If you're a caffeine-drinker, caffeine allows mercury to pass through the cell walls much easier, according to Dr. Boyd Haley.

I hope this helps as a possible explanation for what you're experiencing. I've found that Algin works great for eliminating the ringing in my ears that I almost always experience after drinking tea (regular black or even green tea, since I'm not a coffee or soda drinker).