+1 for the faulty ballast! Had exactly same symptoms on my 2003 3.0. I have strong electronics troubleshooting skills, but was unable to pinpoint root cause issue. Noted that issue has started two weeks after retrofiring used OEM HID lights. Since this was the only recent electrical upgrade - I disconnected both Lo beams - Problem resolved! Ended up installing aftermarket ballasts. Works perfectly for close to five years.

__________________

2012 X5 x35i My new toy
2005 X5 4.4 Her's (Retrofitted Servotronic Steering Rack)
2003 X5 3.0 Mine (Retrofitted Servotronic Steering Rack and Heated Steering Wheel)
2001 M5 Son's car
2000 540i 6sp Sports pkg, supercharged. Son's car (Sold)
2001 530i (Sold)
1999 528i (Sold)
1975 2002 (Sold)