Hey, folks! I have this annoying little trouble - when picking open E string it has some metalish echoe on the top end of sound. Like... well you know... as if you eat something and there is sour taste on the tip of the tongue. On unplugged bass there is no such sound - clean bell i hear when I put my ear to the body of the guitar. On all other strings and while E string is on fret - all is OK. What could it be and how to solve?