One of my first installation trips when I went to work for Gress-Miles was a largish 3 manual in a large Catholic church in NJ. It was impressive enough with that "Agressive-Miles" voicing in the reverberant room but one of the regulators would jump into vibration when large chords were played - they used diaphragmatic regulators like Midmer-Losh. The top would vibrate vigorously like a woofer cone, shaking the whole gallery at some undefined 32' pitch. Quite impressive if you didn't know it wasn't supposed to be there - almost like a diaphone. We were tempted to leave it that way but we fixed it.