I had an A3 sline with the xenon lights and on bumpy roads they seemed to flicker I took the car back it was checked and was told no actual fault found, but was told that the xenons have a shutter type mechanism that changes from dipped to full beam, and there may be a bit of movement on the shutter on bumpy roads, I has the car for about 2 years never had a build failure, then has an A5 with xenons, never had and issues at all, then my first Q3 and again some flickering on bumpy roads, checked at dealer again told probably slight movement in the shutter causing the flicker, on my current Q3 not yet noticed a problem but to be fair haven't been out in the dark much. That said the flickering was only slight, and certainly would not put me off having the xenons, I recently drove an A6 with normal halogen light and couldn't believe how dim they seemed.