Off and on vibration on Bach 42B

[Kernyl]

Hi,

I'm having a weird issue with my Bach 42B w/original Thayer valve. The day before Easter I took it out to practice and it was making a sympathetic vibration when playing. The valve felt a little clunky so I thought maybe something was off there. I disassembled the horn and then put it back together, it was still doing it some on B natural in 4th, especially when attacking the note, but then went away.

Next day I had an Easter gig and the horn was fine. But then a day or too later I took it out to play and the vibration was really bad. Same thing took it apart, put it back together. The only thing that stopped it was to hold onto the bell (outermost part by the solder). So I made an appointment thinking it's the solder coming loose, they're booked for a while, so I guess I have to wait and I've been playing my 36B. But I just took my 42B out again just to check...and now it's not doing it.

I can't figure out why it would come and go. I just had it in the shop in February for a professional cleaning, and it was playing really well after that so not sure what's up. Any ideas?