The key word - when it comes to audiograms - is "normal". An audiogram is concerned with the ability to hear speech. As long as you are within the 0-25db range for 0-8 kHz, your hearing is considered normal. But that does not mean that your inner ear is not damaged in some way. There is no way to really link an audiogram with tinnitus. An audiogram was not invented for that purpose. The person who comes closest to really linking the two is Dr. Wilden. He has several websites; the one below, is the German version:
http://www.dasgesundeohr.de/tinnitusaudiometrie.htm
He essentially explains that already with a db-loss of 10 or more, your inner ear function is "challenged". To understand why that is, you have to remember that the energy carried by a sound wave doubles for every 3db. Put another way: a 10db loss means that a sound wave has to be 3 times "stronger" in order for a person to hear that sound with the same intensity as someone who has 0db hearing loss. So a 10db hearing loss may look "innocent" on an audiogram, but in reality it is not. [This is something I have had to explain to many ENTs during the past year - and they all look equally surprised each time; perhaps because I am educating them, or they simply don't get it?]
I have met dr. Wilden four times. I would describe him as "very passionate" about the topic of hearing loss and laser therapy. Once he "gets going", he cannot stop talking about the subject. Perhaps the most important lesson I have taken away with me from those conversations is that in +90% of all tinnitus cases, the cause is damage to the inner ear. Even if the audiogram looks "normal"...
I am not surprised that your other tests came back normal. They nearly always do in tinnitus cases.