Just noticed this. Not sure how it's getting in there or how to get it out. It's seems to be inside the metal portion of the fender. Not just the plastic flare. Anybody?
Seal your fender liner and panel joints with housing silicone. Get the best you can it is cheaper (x1000) and works better than RTV. You can get it in black also. Clean it as best you can before applying. Areas like this are what cause parts to rust out. Keep it out if at all possible.