See if it does that with another game. Also, check to see if the disc is scratched. If it's scrached, it may need to have some polising done- I've heard it can be done with toothpase (but be careful- do it wrong and you're out a GOTY Oblivion.)
Disc is not scratched it is in perfect shape, Disc a and disc b both do the same thing. Every game I have tried has worked so far, except oblivion.