Short dated spontaneous ringing in ear
Spontaneous ringing is caused by When the outer hair cells put energy back into the vibration, which is known as positive feedback. The process is meant to amplify very quiet sounds more so than loud ones. Normally this works, and you would not notice the sound. But occasionally, the amplification level of one or more outer hair cells will go awry and as a result, the whole system will erupt into spontaneous oscillation.


When this occurs, it becomes audible to us. We perceive it as a ringing in the ear, or “sudden-onset ringing tinnitus see here”. As with most of our biological systems, there are quite a few homestatic control mechanisms (negative feedback) which exist to correct the problem and get rid of the oscillation. It takes about 30 seconds for this mechanism to begin, and then sends messages which suppress the ringing. After the message is sent and received, the tinnitus percept begins to fade away.  You can tell when this reaction has taken place as its often accompanied by a slight reduction in hearing sensitivity (like background or ambient noise we hear suddenly getting quieter), followed by a feeling of fullness in the ear. It usually takes about a minute for this process to fully complete.

Sources: 


Wikipedia. Wikimedia Foundation. Web. 30 Jan. 2016 (https://en.wikipedia.org/wiki/Tinnitus)
"What Causes Spontaneous Ringing In Our Ears?" Zidbits. Web. 30 Jan. 2016.
"What Causes That Spontaneous Ringing in Your Ears?" Sciencedump. 2015. Web. 30 Jan. 2016.
"Tinnitus." [NIDCD]. Web. 30 Jan. 2016. (http://www.nidcd.nih.gov/health/hearing/pages/tinnitus.aspx)