It may be that single click in the bottom center of your touch pad is interpreted as middle click. I have a touch pad that does this, but it's a feature to me,

It may be that single click in the bottom center of your touch pad is interpreted as middle click. I have a touch pad that does this, but it's a feature to me, so I never looked into how to disable it. If the mechanical pressure necessary to click is too much, that's a hardware issue, so not much you can do there. I worked around it by enabling tap-to-click, which works fine for me, but I tend to keep my palms away from the track pad while typing.