Tinnitus (pronounced "tin-it-tus") is an abnormal noise in the ear (note that it is not an "itis" -- which means inflammation). Tinnitus is common -- nearly 36 million Americans have constant tinnitus and more than half of the normal population has intermittent tinnitus.   Another way to summarize this is that about 10-15% of the entire population has some type of constant tinnitus, and about 20% of these people (i.e. about 1% of the population) seek medical attention (Adjamian et al, 2009). Similar statistics are found in England (Dawes et al, 2014) and Korea (Park and Moon, 2014).
Every person living with tinnitus hears a unique sound. The sound can be a low or high frequency, and its volume and pitch may change over time, with the severity varying from person to person. Those with acute tinnitus may struggle to sleep, focus at work, or communicate with others. In such cases, treatment plays a crucial role in helping an individual regain control of his or her life.
Objective tinnitus is very rare. It can be heard by a doctor either using a stethoscope or by listening very closely to your ear. It occurs rarely and may due to involuntary muscle contractions or vascular deformities. The sound is often described as pulsating and may be heard in time with your heartbeat. Objective tinnitus usually has a determinable cause and disappears when treated by surgery or other medical intervention.

Along the path a hearing signal travels to get from the inner ear to the brain, there are many places where things can go wrong to cause tinnitus. If scientists can understand what goes on in the brain to start tinnitus and cause it to persist, they can look for those places in the system where a therapeutic intervention could stop tinnitus in its tracks.
FACT: Some companies will try to point you to a miraculous tinnitus cure where a few pills will stop all signs of tinnitus. While much research has been done around the effects of medication and vitamin supplements on tinnitus, there is currently no proven tinnitus cure.  Only tinnitus management devices and sound therapy have been proven to decrease the effects of tinnitus.
The accepted definition of chronic tinnitus, as compared to normal ear noise experience, is five minutes of ear noise occurring at least twice a week.[50] However, people with chronic tinnitus often experience the noise more frequently than this and can experience it continuously or regularly, such as during the night when there is less environmental noise to mask the sound.
Tinnitus is the perception of sound when no actual external noise or sound is present. It is often referred to as “ringing” in the ears. I have even heard some people call it “head noises.” While ringing sounds are very common, many people will describe the sound they hear as buzzing, hissing, whistling, swooshing, and clicking. In some rare cases, tinnitus patients report hearing music. I hear about 2,000 crickets all going at once! 
Subjective tinnitus is the most frequent type of tinnitus. It can have many possible causes, but most commonly it results from hearing loss. When the tinnitus is caused by disorders of the inner ear or auditory nerve it is called otic (from the Greek word for ear).[25] These otological or neurological conditions include those triggered by infections or drugs.[26] A frequent cause is noise exposure that damages hair cells in the inner ear.

About 25-30 million Americans have tinnitus as a condition, and they experience these noises on a regular, most often daily, basis. About 40 percent of people with tinnitus hear tinnitus noise through 80 percent of their day. And for a smaller group of people—about 1 in 5, tinnitus is disruptive enough to significantly interfere with daily functioning, becoming disabling or nearly disabling.
About six percent of the general population has what they consider to be "severe" tinnitus. That is a gigantic number of people ! Tinnitus is more common with advancing age. In a large study of more than 2000 adults aged 50 and above, 30.3% reported having experienced tinnitus, with 48% reporting symptoms in both ears. Tinnitus had been present for at least 6 years in 50% of cases, and most (55%) reported a gradual onset. Tinnitus was described as mildly to extremely annoying by 67%.(Sindhusake et al. 2003)
While there may be a wide range of causes, an important underlying factor for the development of tinnitus is brain plasticity.5,7 This property allows the brain to change and adapt, and it is essential to how we learn. Unfortunately, in some cases, such as with hearing loss, the auditory part of the brain may be altered as brain plasticity tries to compensate for the abnormal auditory inputs. This response leads to changes in brain activity in the auditory system (e.g., the auditory cortex) that can create a phantom percept: tinnitus. As such, while tinnitus may begin a problem at the auditory periphery, it persists because of changes throughout the auditory system. Treating tinnitus may require addressing both the initiator (e.g., hearing loss) and the driver (changes in the auditory brain).
For some people, the jarring motion of brisk walking can produce what is called a seismic effect which causes movement in the small bones or contractions in the muscles of the middle ear space. You can experiment to find out if this is the cause by walking slowly and smoothly to see if the clicking is present. Then, try walking quickly and with a lot of motion to see if you hear the clicking. You can also test for the seismic effect by moving your head up and down quickly.