On both the right and the left side of the slider there seems to be a 1 pixel vertical line. Normally with a slider background it wouldn't be noticed, but with an entire white / light site it's easily seen. I have png centered images and use the site's background color as the slider background. So, it's easy to see the lines.
I include 2 screen shots from both sides with no background in the slider. In the image below it looks grey, but it's actually solid black. Screen shots are taken from your default template (no mods) and removal of the slider backgrounds.
The lines are coming from ta_swiperslider.css border.
.swiper-container {
position: relative;
width: 100%;
height: {theme="slider_customheight"}px;
min-height: 351px;
background-color: {theme="page_background"};
border: 1px solid rgba(0, 0, 0, 0.8);
border-width: 0 1px 0 1px;
The last two lines (border and border-width) are causing the lines.
Just wanted to let you know. I removed the lines in my custom.css.
.swiper-container {
border: none !important;
}