Fiberglass separating

[dmcindiana]

Hi, everyone. The entire time I've had my car I've been getting a noise from the passenger side of the firewall. Super hard to pinpoint the source. It's only when I go over really rough road at low speed. The best way to describe it is the sound you'd get if you took a sheet of fiberglass, damaged it to create a long hairline crack in the middle, and then grabbed the edges of the sheet and flexed the sheet back and forth so you got a clunk along the crack with each flex.

I finally had a chance to tear out insulation and drop the top trim panel the holds the rear dome light, and I can't find any obvious damage whatsoever. The rear window is quite solid in position as are both engine cover hinges. Nothing moves with poking with objects and light tapping with a hammer all over the place.

Please see the photos. What experience does everyone have with this seam separating? It looks like the normal gap between two adjacent pieces that's overlaid with RTV. Has separation here been common or is it becoming a new normal here at the 45-year mark? Could a microscopic separation here be enough to get the "sheet flexing" sound I described? What's the remedy?

Or is there a common damage/fatigue spot I'm not looking at, not related at all to the seam in the photos, that's at the passenger side of the firewall?

7184671847

[David T]

Push on the fiberglass at the bottom of the rear window in the middle. Not uncommon for the glass to come undone from the fiberglass and it looks like it is bonded. Also check that the plywood is still bonded to the fiberglass behind the passenger seat.

[dmcindiana]

Cool, David. I'll refocus on the center area under the window and report back.