I got tinnitus in 1999, working on one of my very first mastering projects the day I opened my studio, JR mastering.  At that time, I needed to listen to the songs much longer than I do now because of my lack of experience, and I listened to them WAY too loud. 

I was reviewing my final masters at a high volume level (105-110 dbs) for about 30 minutes non-stop.  When I was finished I didn't really notice anything.  But, when night time came I could hear a high-pitched tone.  It sounded like a 40db test tone @ 5k.  I could hear the tone in both ears, but my right ear was twice as bad as my left.  The first few days it was hard for me to sleep because I kept thinking about this sound.  The sound was also very annoying when sitting outside in a quiet area.