I have no clue where they come from, but they are annoying. Thankfully, they don't seem to cause issues (but I'm not sure if they do, as I clear 'em out as soon as I see 'em).

A good dousing of systemic pesticides (imidacloprid) or spraying all plants/plant parts down with a mix of 1/4 cup rubbing alcohol and a squirt of baby shampoo or dish soap (not detergent) to 25 oz. water works. You will have to reapply the alcohol spray, as needed, until the gnats disappear. Be sure to leave any plants treated with sprays/chemicals in a low lit area, until everything is completely dry.

thanks, im also gonna make some traps but i'll try your spray as well