In reply to subtle:
I'd put some light lube on each point where the spokes cross, and and see if anything changes after wiggling them a little to work the lube into place.
I've literally had the same issue with a back wheel, and it was two spokes 'clicking together' with each revolution. It drove me nuts, I can't work out what solved it in the end, I might have just tuned out the noise?
A catastrophe hasn't happened since, so there's that to keep in mind.
Post edited at 22:30