http://tijil.org/Scion_Docs/Scion_TSBs_thru_AUG06/ax01104.pdfAX011-04 FOG LIGHT VIBRATION
12/1/2004 - 2004 model year Scion xB vehicles. Some 2004 model year Scion xB customers may complain that the fog light vibrates while driving. The following two causes have been identified:
1. 0.5 mm (0.02 in.) gap between the bumper and boss of fog light.
2. The tabs of the fog light adjuster and the alignment pin are not completely seated.