OK So I've managed to have luck with what I thought was a busted trackpad, and cost be about 5p.
I tried most of suggestions on here with no luck.
First download BetterTouchTool, its free. Its designed to add more functionality/gestures to the trackpad. It has a very handy feature - live view. This shows what the trackpad is sensing at any time. You can use it to help diagnose the problem.
For me, I had a constant iterference in a horizontal line about halfway up my trackpad. It would make the computer think it was constantly being pressed, causing all kinds of annoying madness.
I voided my warranty a long time ago (putting in a 2nd hard drive in place of the cd drive) so had no problem opening it up and having a tinker.
If you do open it up, be warned it may void your warranty, so if possible just get apple to have a look first.
These are my steps:
- turn over and take out all the screws on the bottom.
- Unscrew/ unplug and remove the battery.
- Unsrew the 4 screws holding the trackpad in place and 'pop' it outside of the case (so when the laptop is upright it is out of the case.
- Take this opportunity to thouroughly clean everything, as its much easier when its apart.
Now what I noticed was, after turning it back on after plugging it into the mains, it was working. I put BetterTouchTool into live mode and saw nothing.
In this state I started to play around with the trackpad to see what was going on. What I found was that by touching the dotted metal underside of the trackpad it caused it to kind of 'short', touching any point would result in the same horizontal interference.
Then trying with a bit of trial and ever to gently place the trackpad back into place I decided it was shorting out on the part where the screws attached it to the rest of the laptop.
So
- Get some electrical tape and just cover the two metal fixtures (that have 4 screws in a line).
- You should still be able to screw threw the electrical tape after pricking a small hole in.
For clarification, and help of how to take it apart you can use this guide.
http://www.ifixit.com/Guide/MacBook+Pro+13-Inch+Unibody+Late+2011+Trackpad+Repla cement/7664/2
step 12+13 show the part I am talking about.
Now this works for me and have had no problems since. I cannot say whether it will help you, but due to the fact you have to take it apart it may not be a fix for everyone. So just be careful and make sure you check to see what BetterTouchTool shows you.
I really hope this helps.