Have you recently changed your light bulbs and now have noticed that they randomly flash when starting the engine?
When the vehicle is started, the more up to date BMW's and quite possibly some other manufactures run a bulb check to make sure all lamps are functioning. To do this the vehicle runs a continuity test, i.e. putting a low voltage through each of the bulbs. If a bulbs filament is broken (bulb blown) then the current sent out does not get returned (no continuity) and the vehicle identifies a particular bulb is no longer functioning. For the standard Tungsten type bulbs used, as the voltage within this test is very low it is insufficient to power up or illuminate the bulb, so the test is carried out unnoticed. However, LED type bulbs use much less power and in this case the continuity test voltage supplies enough power to intermittently illuminate these LED bulbs and they will start to flash.
Is there a fix?
Yes. You can have the continuity test disabled and there are two ways to do this. The first is to buy a ELM 32 connector to plug into your OBD port, then to purchase a downloadable app from Google or iTunes called Carley and do it yourself. Both the ELM connector and the app will cost you. Option two is to ask your local garage/BMW dealership to do it for you.