What would cause my headlights to flash

I have a 98 pontiac transport, my wife coalled me at work to tell me that upon starting the van as soon as she dissengaged the e-brake the headlights began to flash and flicker steadily. If you turn on the running lights or full lights the ticking is still there but the lights stay on. I checked all fuses and bulbs appear to be functional. Anyone seen this before, what should I look for.

Thanks

DO you mean they go from fully ON to fully OFF or just change in intensity?
As a first investigation, I would install a voltmeter may be using a plug in the cigar lighter to see if voltage fluctuates all across the system...