What Causes Metallic Taste In Mouth With Twitching In Brain?

My wife has had a metallic taste in her mouth for going on 2 years. She also hears her heartbeat in her head especially at night when she lays down. She also has what she describes as a twitching in her head or brian. She has experienced places of numbness in areas like the side of her nose and her pinky finger for a period of time but not long lasting. She has seen a neurologist and has had an MRI of her head which came back negative. She has had a multitude of blood tests to check for metal levels and vitamin levels. Both did not show any abnormalities. She says that the metallic taste is constant but does not effect eating. It bothers her horribly and she is incredibly frustrated with the lack of diagnosis. Any help or guidance would be appreciated.