Years ago I nailed my stand with a solid Dbl. C from about 3 feet. It broke most of the welds. The stand is now deceased and I have to memorize everything. Sympathetic vibrations are common in small rooms. Usually a trumpet in close proximity to a snare drum will do the same thing. Glad you figured it out. Hope your range returns as well. Good luck. You now are aware even though Yamaha horns are awesome, no 2 are identical. Always play a few of the same horns if possible, then buy the one you feel is the best.