Pay close attention as to when it flickers. It COULD be a connection issue, although this is somewhat unlikely on an oem install.
-Does only one side flicker, or do both?
-If so, is it always the same side?
---In the above mentionned case, move the bulbs from left to right.
-If the same side still flickers, and intermittantly/randomly (not only when you go over bumps), its a ballast issue.
(shameless plug AbsoluteHID Replacement Ballast
If the flickering changes from one side to another when you swap the bulbs, its a bulb issue, D2S bulbs
If you have anymore questions, let me know.
Hot: 2001 Estoril M Roadster
ZCP 19's, ZHP knob, JL 8W3
Cold: 2002 TiAg M3 6mt
ZCP 19's supersports, ZHP knob, UUC short shift GROM, OEM 18's w310's,
http://absolutehid.ca hid kit