Sounds like the sensors in the screen acting up. Which is in effect simply a sign of the tech getting old and worn out. Sadly phone manufacturers build each handset to last between 12 and 18 months on average. Making it all 24 months of your contract without some major visible marks and some glitches to both hardware and software is almost impossible.

Time for an upgrade Pike. Don't worry though the newer Samsung handsets are pretty nifty.

Personally I'm not sure what to choose in the summer when my upgrade is due.