Analog Stick Issues

[gotex007]

So I'm using a standard Microsoft brand Xbox 360 controller and for some reason with both sticks, there's an issue where a few degrees when pressing down/left near the "corner" it wigs out (like I slowly move it more left and I go from going southwest to south to southwest again) and sometimes becomes non-responsive as if I'm not pressing it down.

This might not be a very good explanation for the problem I'm having, but it has cost me a lot of points in Hot Shots Tennis. Is there anything I can do about the issue? I've sat and verified that it isn't my controller that's the problem by staring at the calibration information as I slowly rotate the stick. It's also only southwest I believe.