I've had tinnitus for 2 years. in the evening when i get tired, the sensation of metallic taste in my mouth arises, why is that ?

Metallic taste: The taste may signal a leaking restoration that needs replacing. I have also seen taste altered by medications especially those that also cause dry mouth.

Metallic taste: A review of your medications could reveal a possible cause. Check with your md to see if a medication has a known side effect or if you have a symptoms of reflux that may be the cause. A follow up with your dentist to evaluate your teeth for failing restorations would also be recommended.