Here's something we see a lot of in attics. It's the duct system starter set that some outfit did many of in the late 80's. That grey plastic deteriorates in hot attics, exposing the inner lining. Calls are usually due to water leaking through the ceiling or staining due to sweat on exposed liner. I think the triangle boxes were available through hardware stores at the time. Last one was a homeowner's attempt to solve with duct tape.
Always a good opportunity to install a proper duct system to solve the problem.