What Causes Buzzing Sound In The Ear?

HI, MY HUSBAND HAS BEEN SUFFERING WITH RINGING IN LEFT EAR. LIKE A GENERATOR RUNNING AT A HIGH PITCH FOR ABOUT 3 WEEKS NOW. HE ASSOCIATED IT WITH HIS WORK, VERY NOISY. HE WAS DIAGNOSED WITH POSSIBLE MS. 5 YEARS AGO, BUT HAS BEEN WITHOUT SYMPTOMS FOR 3 YEARS. CAN THIS BE ASSOCIATED WITH MS. AND SHOULD HE SEE A NEUROLOGIST, OR WHAT TREATMENT CAN HE USE FOR RELIEF. IT IS DRIVING HIM CRAZY AND NOT SLEEPING