Why is phone shutting down/unresponsive when pressure applied to top?

A little after performing a battery replacement on my iPhone 4S it started randomly shutting down at times with any given battery percentage remaining. It would only turn back on after I connected it to a power source at which point it would boot up and display whatever battery power was displayed before the shutdown. I searched everywhere for answers and did all the classic fix attempts; full restore, firmware restore, hard reset, etc. etc... but to no avail. Just recently, I seem to have isolated why the shutdown occurs, but have not been able to find an answer as to why it might be the case. It shuts down this way whenever I apply a certain amount of pressure to the top part of the phone (near the camera/earpiece ). Was hoping I could have some answers so maybe I can stop this from happening! Thanks!