Display on phone acting glitchy

The display on my phone is acting "glitchy". One minute it will look fine and the next it will be sort of wavy/shaky. Is there any way to determine what might be the cause or how to fix this? I have a Samsung Galaxy S4 phone. I tried deleting some apps thinking that they may be taking up space/power but that didn't seem to work. Other suggestions I can try? Thank you.
