I had new shutoffs and new flex supply lines installed by a professional plumber a few months ago. Today, I installed a new faucet because mine was very old and starting to fail. I installed everything successfuly however I am now noticing an extremely minor leak in my cold water supply line. Basically, I can run the water for 5 minutes and nothing would happen but when I shut off the water at the faucet, a few seconds later, I get a tiny drop of water build and drip from the area I outlined below.
I didn't disconnect the supply lines from the shutoff values when installing the new facuet so I figured that maybe I losened it slightly by mistake during installation. I tightened it as much as I could, just to be safe, but the problem seems to still be happening.