Vibration transfer from the motor, or nearby sources of such, like a railroad etc.?? I put CFL's in Mine, been there for well over a decade, but those are yesterdays news now. I've had spotty luck with LED quality, expensive or cheap,..had both take a sh*t prematurely and last for years now........same went for the CFL's.....I've tried bulbs from entirely different states, with no change. I even added vent holes to the bases to get more cooling air flow















