Well thermal grease is made just for that reason, to dissipate heat , or conduct it. So it could be possible. By googleing the 5150, you will find many articles of heat issues. Not unlike any other laptop.
If the artifacts get worse, that I would assume is a heat issue, or , the power supply has a greater demand as the system loads , so you could have a couple issues. You may want find out where everything is at. There is a good program called "everest", there may be newer , or better, but none the less, it reveals a plethora of info on your machine.