Sealing up the last of my supply vents (mastic between the drywall and the sheetmetal boot). Vents and boots are 30 years old (with the house), all-new AC/furnace/air handler and flex duct to the boots 4 years ago. All equipment and duct work in (recently more) ventilated attic.
A few of the grills were somewhat dirty, and a few had a few spots of mold (that were cleaned and bleached). This last vent had a good bit of mold on it, some of it fuzzy, covering 30-40% of the inside-facing surfaces. Wish I took a picture before I cleaned it off Well, no I don't This particular vent is directly below the (both old and new) air handler assembly.
Short of a professional inspection (and porbably ripping out some ceiling, which I'd like ot avoid), any reason for concern here? The old system that was replaced was in poor condition, and was replaced within a year of moving into the house. I'm imagining some condensation/moisture worked it's way down.