Disturbing white line in header

Hey, on my website https://www.sycosoltemp.com there’s a white bar, a few pixels height, overlapping on the grey background of the header. Just above the photo slideshow.

I tried adding a gap below the navmenu, add a gap above the slideshow, but there’s still this white bar on the bottom of the grey menu, it makes it look cheap… please help me get rid of it, i’m desperate

thanks a lot