Obviously there is s humidity problem. In what part of the country is your garage?

Years ago, some laundries vented into the garage.

Garage is in New Jersey. The laundry doesn’t vent into the garage. I’ll have to look for something else. There are hvac ducts in the ceiling. Maybe one has a hole.
Thank you

I see it in mine in the Springtime. Cold temps at night, combined with warm humid air moving in during the day. Just enough condensation will form that rust can develop.

Having lived there for so long and the issue appearing only recently, something has changed. Perhaps the seals of the garage door need replacment.

if you can, monitor the temperature and humidity. Generally even an uninsulated, closed, attached garage will be several degrees warmer than outside air temperature. Therefore condensation is somewhat limited.

I've noticed the same problem. But I live in Arizona where the humidity is low and the air is dry. I never had this issue when I lived in the Northeast where the humidity is fairly high. Could be all the junk metal made in China.