I have exactly the same problem. Anyone know how to fix it? 

Remove the base cover and carefully check the battery (directly under the touchpad) for signs of swelling.  If it's swelling, remove it and dispose of it immediately.

A raised touchpad is indeed an indicator of a swollen battery.  An even earlier indication is a touchpad that's difficult or impossible to press.

Thanks @ejn63 . That makes sense, I will open it up ASAP and inspect it. I've been in there before to replace the power jack.

Thanks, the touchpad is not raised up in that area, which I read is an indication of battery swelling but I will check it out internally ASAP.