HID bulbs are like miniature fluorescent lamps or UV curing lamps, where they fire the two electrode ends to excite the mercury into plasma (where you get the insane bright light), so if there is a crack in the quarts glass and air gets in or mercury leaks out, it can still "fire" as it is trying to light the gas, but no plasma, so that may be the little spark you are seeing.
Get the Darkbuster 24watt HID - same price, better features, (a little higher, actually on Scubatoys), but at 1750 lumens, its over 4 times brighter, and I hear it has a more robust bulb (mine is still good).