1989 s-10 metallic clatter in dash, driver's side on 1990 Chevrolet S10

My truck just started making a noise like two metal plates rattling together when I hit bumps in the road. It's a loose sound, and seems to be coming from inside the dash, driver's side. Any ideas?? Thanks.

Asked by for the 1990 Chevrolet S10
Rattles can be very tough! The noise could be something hitting the firewall from inside or outside. Road test with someone so that they can concentrate on the noise and not worry about driving at the same time. See if you can duplicate the noise while stopped by taping various places around the firewall area. Try and make sure it is not a suspension noise which just sounds like it is from the inside.
Good Luck!
Don't feel bad, I know a story of a dash rattle where most of the dash was removed looking for the problem. It turns out the sunvisor was not secured correctly and was hitting the windshield. It's something how that sound can travel down the window and sound like it's comming from behind the dash.
Hi Russ, Fully aware that this will expose me for the automotive doofus I am, here's the answer. : ) At home, we got up under the steering wheel, reached around, looked for anything loose, found nothing. The next day, I drove all day with No NOISE! The mystery was making us nuts. The next time we went out, what? Wait! There it was again, just once or twice. But I immediately pinpointed the sound, and folded my visor up against the cab roof. There, pinned for months, was a tin campaign button. It had been pushed close to and was rattling against the window. Made us laugh out loud, and feel very, very foolish. Thanks for your kind attention.
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Heater Core - Mine is still doing it. Oh by the way is there a bubbling sound when accelerating? <grin>
try a springwasher at the hood hinges, swedp