Looks to be in time with the fan rotation (hitting shroud?) - water pump
bearing or fan clutch.  Don't let it come apart and drill into your
radiator.

If not that, check belt tensioner pulleys.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

I had a bad sound like that with my 1993 Voyager. It turned out to be
the water pump. It sounded like a high pitched rattle sound, as
opposed to a worn bearing sound.

I would also suggest checking the fan clutch as Bill suggested.
Perhaps you could remove the belt and run it for a few seconds to see
if the noise goes away. Any one have any other suggestions to diagnose
a worn fan clutch?

-KM