I have tinnitus. I am only 21, which it is usually uncommon for people of my age to get tinnitus. Mine was caused by excess sound pressure. Apparently, putting your ear up against a sub woofer can damage it
Like you, I have various different tones - but they are constant. They are more obvious when it is quiet and when I focus on it.
Anxiety can cause tinnitus - fact!
I don't want to worry you, and bare in mind that I am in no way a doctor, but there is a type of brain tumour (but it is benign) called an acoustic neuroma which can cause tinnitus. But there a load of other symptoms that you would experience too. Not only that, but because it is a slow growing tumour, it would take a considerable amount of time to grow to a size to cause other symptoms associated with intracranial pressure (headaches, blurry vision, vertigo etc.) and I don't think tinnitus alone should be a cause for concern - other than the fact that persistent ringing can obviously cause stress and frustration.
If your tinnitus is caused by your anxiety, I wouldn't worry at all and it may (not definitely) fade away. If it is caused by actual damage through long term exposure to loud music, although this can be distressing, I have it and I am over the stress; but I would suggest protecting your ears from now on (if this is the cause).
Based on the fact that you not only describe different frequencies, but you also experience different sounds at different times? This tells me that it is shifting more to a symptom of anxiety than that of a benign brain tumour.
If you think you need to, get it checked out to definitely rule out any serious causes - but I wouldn't try to worry about it too much if I were you. It is most likely going to be fine and no cause for concern. :)