unwanted lines

hello,

with views (grid) and using table and teaser, i get :
a grey horizontal line with firefox and IE
(not the one of the grid created by Views (i want to have) but one coming from each node called by Views, having table/tbody and the teaser)

on every content, i get also a grey horizontal dotted line with IE (with or without any table or teaser or ...)

cf screenshot joined

i tried to find where it could be in css with firebug, but ... ??? :(