One of my HVAC vents in my ceiling was chipped and painted over so many times I wanted to replace it. I bought a simple one at the store and went to screw it into the ceiling, but it appears that after screwing past the drywall ceiling, it it hitting the duct. The holes are in a bit different place than the previous and I can't tell if the old ones went through the duct. Is that normal? Any harm putting the screws through the drywall and into the duct?