I was in the middle of cleaning my gsg 522 pistol and I heard something rattling in the frame and a tiny set screw fell out. I had already removed the trigger and bolt group when this happened. Does anyone have any idea where it goes? This thing is tiny I'm guessing 2-3mm, it fits the smallest hex key that comes with the gsg.

There is always some extra screws when you reassemble a firearm.

You should see what I have left over after I rebuild a motor.

I'm starting to wonder if it even came from the firearm. I looked at an exploded parts view of the gsg and didn't see anything. The closest thing was under the hand guard to pin the barrel but that on is definitely longer.
I'm starting to think it was an extra screw that maybe stuck to a tool I was using. It looks like a set screw for a gas block on my AR.

Check the bottom of the front sight.  On mine there was a small threaded hole for a set screw to hold on the fake suppressor.  It was a 3mm IIRC and now holds on the 3 lug adapter in place.