Did you fit the self levellers in your install?
Have you checked the rear of the housing to make sure the bulbs are still latched and seated properly and that the projectors aren't loose inside?Also it's possible that it's flashing because of a coding issue and working the shutter for the Bi-xenon?
This may help youhttp://forums.vwvortex.com/showthread.php?3179017-Purchased
Are you sure you don't have damaged headlights? The interior mechanism shouldn't be loose when you shake the headlight.
Is it the headlight you had to replace all 3 fixing mounts by any chance?
Well IMO thats where you start, i'd pull the light out and check the mounting points, sounds like the install of the mounts needs looking at?