No more than a day or two?! That's gotta be annoying!!
How about using a CFL, just to see if this will last?
Ok , Not such a good idea if excessive voltage or TVS problems, but it would work for an unstable area (i.e. excessive vibrations or random thumps from something on the roof / floor joists).
If there is absolutely no way this could be caused by some physical item(s) rattling the filament to death, then you have got some troubleshooting to do!
If 1Ø, suspect open noodle. If all noodles OK, try any lightly loaded Induction Motors starting, and see if a noticable increase in Line Voltage results when started and / or run.
One situation where low wattage Incandescent lamps are driven on the opposite L-N circuit as a lightly loaded Induction motor being started - and where they share a common noodle, the Incandescent lamps will get brighter as the motor starts, and they will taper down to normal intensity as the motor KVA load stablizes.
That's probably too extreme for your scenario, but worth a shot if all else fails.
Failure within 48 hours pretty much sums it up to either:
[*]Repeated Overvoltage Surges,
[*]Something is shaking the hot filament too much!
Could water be dripping on the lamp?
Could the neighborhood kids be overly obnoxious?