What is blue/pink lines flickering (but external monitor works great)?

My MacBook Pro started to have these blue or pink vertical lines, sometimes both, flickering on the screen. First, I thought it was the video card, then I plugged an external monitor, but the on the monitor it works as it should work.

I'm not sure which is the defective part of my mac, if it is the display data cable, the inverter, or another that I don't know.

One of the interesting things is that if you slightly bend the body part (not the display), sometimes the problem disappear, but only if you keep bended.

I've done a lot of research, and it seems to be a very specific problem, so I really need help! As soon I have the idea of which part should I replace, I will buy and replace it myself, since the warranty is long gone.