What you described sounds like tinnitus. Usually, a high pitch ringing sound is a form of subjective tinnitus. Given your history of previous exposure to loud noises, your tinnitus may be due to hearing loss (which may be mild and not noticeable by you).
Fortunately, the majority of the time, tinnitus is not due to a dangerous condition. We do not fully understand why it happens, but there are theories that it may be due to the hearing nerve misfiring (e.g as result of damage from previous loud noise exposure) or it may be the brain generating the impulse that gives the perception of a sound.
It is best that you consult an ENT Specialist to have your clinical history taken, and to undergo a physical examination and hearing test.
