HTC Incredible :: Screen Panning Left / What May Have Caused It?

I've had my Incredible for a couple months, and this just started happening a couple days ago. First, my home screens shifted to the left (as if I was doing it with my finger). I would leave the screen on, lay it down on a table top, a few seconds later, shifted to the far left again. I pulled up some things with text input boxes, and again it kept trying to shift the cursor to the left.
I checked and since it's still under warranty Verizon will swap it out. It only happened for a couple days, and has quit since (happened a few days ago). Any ideas what may have caused it? Think it's worth going ahead and swapping it while it's still under warranty? Hate to run the risk of it doing it again later, of course knowing my luck I'll get a screwed up one when I swap it out!