Fluttering lcd, sometimes an issue

So, recently, I've been noticing this issue, and it's very recent for me. Sometimes when I install a display assembly, I get fluttering lines, on the lcd. This isn't the same as when you use cheap parts, and you get those white lines. It's almost a strobing/blinking light. All the colors of the lcd picture are there. But they're doing the strobe effect. It's so weird, and I'm getting really good parts. So, I'm wondering if it's something I'm doing? Could it be my magnetic mat? Which Mav ruled out, in a different thread. Anything? Anybody? Oh, I've been getting this with iPhone 5S and iPhone 6