In most cases that I have seen with trackpads not acting as expected it is hardware, not the drivers. The easiest way to test this (depending on how easy it is to reproduce) is to boot to a known good operating system; i.e.: a different partition containing the OS either one you made or the recovery partition by holding down option and selecting Recovery HD (10.7 and newer). IF it happens there because the recovery partition or triage partition (one that you created) then you KNOW it is hardware. In which case if it is internal, I would say take it to someone to adjust it/replace it... ESPECIALLY if it is a MacBook Air.(They have exposed batteries, when mishandled can cause damage) It is most likely one of a few situations A) Battery needs to be replaced, old batteries expand (it's intended that way) and can cause the issue. B) Debris is in the cracks of the trackpad C) Liquid damage, more cases than not, users cause their own issues D) The trackpad breaks on it's own. Seen this very few times. In which case, you need a new trackpad. Go to locate.apple.com to find someone that is trained to take these units apart, in most cases Apple can reseat a trackpad and if needed, replace it at a cost if not under AppleCare or there is physical damage.