I am a beginner, taking clock repair classes at a tech college. Over the summer, I've been testing a Gilbert bim-bam mantle clock I repaired last class. On what seems a random basis, the first tone "bim" has an extended vibration, as if the hammer is striking the rod while the rod is still vibrating from the previous strike. The result is an echo of the bim rather than a clear tone. The extended vibration hasn't occurred with the "bam." Sometimes, it vibrates correctly, and both chimes are clear tones.
I am not seeking perfection with this clock, just want to understand what's going on, regardless of whether it's repairable. I have tightened the chime rods, fussed with the hammer height, and it still happens randomly. Any comments or advice is welcome. See photo taken prior to repair/cleaning. Thank you.