It sounds like you are applying too much pressure. There might be a couple of reasons for this. You might feel you need to apply lots of pressure to make a clean note - try backing off the pressure until your notes ring clear. You might have a guitar with action set too high or you might have heavier strings than you can deal with. I would try backing off the pressure 1st. If you are able to, a good setup and lighter strings are never a bad thing.

Good luck.