I hear high pitch ringing in left ear, only when it is all quiet - before sleep. what could that be? thank you.

Tinnitus: Tinnitus is a sound originating in the inner ear or the brain itself. When it comes on suddenly,is intense and associated with hearing loss or vertigo, evaluation by an Otolaryngologist is advisable to look for a serious cause like a tumor(acoustic neuroma). However most cases are not serious but are a nuisance and may be permanent. Occasionally ear wax or loud noise exposure is a cause.