I think I have leaves and things trapped in the washout under the windshield wiper blades. Not really much of mechanic but is it much of a job to get that plastic grilling off under the blades to get in there and clean things out. For a while I thought it was the under hood liner vibrating at speed so I re-glued the edges with silicon but hat was not the problem. the washout gutter seems more likely.

2006 FX4 s' crew.

 

Its not hard to get that cowl cover off.. there is a little plastic plug on each side, then you can just pry it off. Just be careful not to break any of the little tabs, they are a pain to re-install if you accidentally tweek it