Silent mode turning on and off on its own.

About 2 weeks ago my phone started going into ring mode on its own, despite the fact that the vibrate switch is in silent mode. I found that if I press on the front and back of the phone in the upper left corner, I can cause it to vibrate on its own. At this point I have turned it to ring mode because the constant switching between the two modes was running my power down. It has not been dropped, or gotten wet. It really just started happening out of the blue. My question is whether I need to replace the switch or the vibrator. Any recommendations?