Trackpad goes crazy sometimes

Every so often, usually after being stowed in my backpack with a padded pocket and a second padded sleeve inside that, the trackpad goes nuts, cursor starts wavering and darting, sometimes all clicks are double-clicks.

Sometimes twisting the body diagonally will stop it, sometimes taking the bottom off and remounting it will work, sometimes giving the trackpad a CPR-style press at the front will work, and sometimes it just takes time.

Doesn't seem to matter whether it's plugged in or not.

Since i have replaced the HD a couple of times (another oddity, but perhaps bad luck), the screws come loose and tightening them can sometimes work, but not always.

I just went around the base with a screwdriver blade to scrape off oxidised stuff this last time, and so far we're back, but it's irksome to not be able to depend upon a working laptop.

I keep thinking that problem is a connection somewhere. All I have done internally is change HD's and reseat the RAM once. I am already missing 3 screws and need to find my Locktite and start using it.

Any help deeply appreciated.