TromboneChat

I recently purchased a used Bach 50 bass trombone with a double axial flow valve setup. It ended up needing a number of repairs, including replacing the inner valve rotor on the second valve. The valve works and sounds great now, except that there is a buzzing coming from that area when that valve is in use. The buzzing doesn't happen anywhere else or at any other time. My repair tech checked all the braces and linkages and we can't figure out what could be causing it. Any ideas?

Check and oil the linkages with a thick oil, and also make sure the stop arm is secure on the rotor spindle.
The stop arm needs to fit tightly before the screw is tightened.

In a double valve set up, there are A LOT of solder joints. A small leak in any of those soldered areas could create a hissing or buzzing sound. A leak can also make the horn rather inefficient as well.

Is the screw ring to secure the two pieces together tight? Tighten it to where the valve does not move freely and loosen it just until the valve works well.

That would indicate to me that the valve is actually not fit correctly. The ring should be snug, the valve should not leak, and it should rotate freely.