Flashing/flickering lights

[derekf]

This is on the wife's car - an 02 Chevy Tracker (rebadged Suzuki Grand Vitara).

Sometimes - and there doesn't seem to be any rhyme or reason to it - the lights will start to flash bright/dim about twice a second. The only real bothersome symptom, to me, with this, is the whining sound from the other person in the car when the flicker starts - but I'd better fix it to make her happy.

Initially it was only off-idle, but lately it'll even do it at highway speeds. My thought would be voltage regulator but those are insanely pricey - Autozone says almost 250$ for one, so I don't want to just start randomly swapping parts.

Anyone have any experience with these/that sort of problem to tell me if I'm on the right track?