OP- I have had nonstop tinnitus since April, 2009. It is aggravated by loud noises, fatigue, and stress. I like to say it started in my "rocker years" but, alas, that would be a lie. I had had it sporadically prior to that time and it would "go away" as the day progressed. On that day, it started and never stopped. Anyway----I also have a hearing loss primarily in that ear and wear hearing aids which actually help. Sometimes if it is too quiet the tinnitus is louder. If i am busy and don't pay a lot of attention to it, it is minimal to non-existent.
As to stethoscope use---unless you have a hearing loss, you probably won't have any difficulty using one. Just train your ear to "hear above the noise" of the tinnitus.