I recently solved a “buzzing” noise problem with my Silent Brass mute. It had been working just fine. Then, it suddenly started making an annoying buzzing noise every time I played a concert Eb. At first I thought I had a loose valve cap. Then I checked all the braces and solder joints. After much investigation, I discovered it was coming from the mute itself. There is a long narrow shaft inside the mute. The mic is at the bottom end of the shaft, and there is a long spring wound around the shaft. I reasoned that the spring might be causing the vibrating noise, so I used a long narrow tool to reach into the mute and gently nudge the spring around a bit. Apparently it realigned itself and the buzzing noise stopped happening. Now, all is well.