Anyone have any recommendations for making metal siding quiet? I'm putting on metal siding that I got free from a local contractor, but curious if anyone knew of maybe some sort of spray paint or something to make it quiet for when it rains.

about all you can do is add insulation behind it to make it less noisy
you can TRY adding some rubberized under coating to it, too,
key to it IMO< is getting a TIGHT fit behind the metal roofing to some sheet foam insulation or spray can foam like, so its not hollow behind things

Yep a sheet of foam insulation is your best bet.

It'll still have some sound. But you won't have that ping ping ping every time a rain drop hits it
​​​​​​-jake