Screen Flickering on Retinal Display
I've tried to reset the PRAM, NVRAM to no avail. Can get clean display via HDMI to another monitor though. Flabbergasted! Are there any safe free MacClean up Applications online?
MacBook Pro 15″
Sounds like the built-in display on the laptop has a hardware issue if an external display is working fine. You will most likely need to have the laptop repaired.
FYI, do not use any anti-virus apps, cleaning/optimizer apps, or third party security software since they are not needed on a Mac. Plus these types of apps usually causes more problems than they solve, plus they impact system performance. See this excellent article written by a respected forum contributor regarding how to keep you computer running smoothly as well as protecting you & your computer:
https://discussions.apple.com/docs/DOC-8841