Trackpad works for a short time then start to move erratically

Hi,

I’ve just done a fresh install to El Capitan with a brand new battery on my MacBook Pro 15” 2009.

The issue i’m having is that the track pad works fine for a while and then after 3-4 minutes it starts to behave erratically making it impossible to select anything.

The only thing that fixes it again for a short time is by hitting it fairly hard, after that it goes back to it weird twitching.

I think i’ve tried pretty much everything….

• Fresh install, happen with both Snow Leopard and El Capitan.

* installed New battery, old one wasn’t bulging

* reset PRAM and SMC (PRAM i got the double chime and SMC the power connector changed colour

* tried with and without the power lead same, same problem

* tried with nothing else is plugged into the computer

* clean it with alcohol and scraped around the edges with a blade

I’m certain it must be a hardware issue as hitting it fixes the problem.

Any ideas welcomed

Thanks