What does he mean by “ends up in the brain”? Essentially, something that causes even temporary hearing damage — such as exposure to very loud noise or a blow to the head — can change activity patterns in the brain in ways that cause the ringing. Even though some damage or problem in the ear triggered tinnitus to begin with, you continue to hear the sound you do because of a signal from the brain.
Atherosclerosis. With age and buildup of cholesterol and other deposits, major blood vessels close to your middle and inner ear lose some of their elasticity — the ability to flex or expand slightly with each heartbeat. That causes blood flow to become more forceful, making it easier for your ear to detect the beats. You can generally hear this type of tinnitus in both ears.