Either your rotors are poor quality or your wheels were not torqued properly (I'm assuming < 10k miles and new pads installed with new rotors).
If it is a mild warp you could try re-torquing wheels.


98 Mystique LS v6 atx 110,000km
97 Contour LX v6 atx 125,000km
stock CD on LS, cass on LX
spoiler, tinted windows on LS only
4 wheel discs on LX only
All other available options on both