He and Rich King both pointed out to me in my audition for the Cleveland Institute of Music that it was something I really have to work on and fix over the next few years; otherwise it could spell big problems for my playing. They said it will "hopefully go away" over time, but this still really worries me.
Ricardo is right about the distance of your lips causing all sorts of strange buzz sounds. It may take some tedious work for you to figure this one out if that's the issue. You'll have to just make the sound you dislike and methodically change aperture size and shape until you get a sound that you like. I always try to keep my aperture as round as possible.
Too much mouthpiece pressure. If you ever get rings on your lips, consider this exercise: Play a single note and simply pull the horn away from your face and keep buzzing. When you're not touching the mouthpiece anymore, return the horn to your face as slowly as possible. There will be a moment that the buzz sound can be heard through the instrument and straight from your lips at the same time. At that moment stop moving the horn and (for most people) the sound will magically start to come only from the bell of your horn. That's the amount of pressure needed to play that note at that volume.
If you suspect that your horn may be buzzing, often that's a leak where something has become unsoldered or a loose screw or spit valve. You'll need somebody else to put their ear right up to different parts of the horn to see if they can pinpoint the sound as you play.
Of course articulations sound best if your air is doing most of the work. As an exercise, practice repeated notes without tonguing at all. If you can get those to sound good, then when you add your tongue back in that may fix it.
If your tongue is really doing something weird, try practicing with earplugs in your ears. You'll be able to hear your tongue straight through your skull. Then you can clean up those articulations.