xbox 360 - fifa 09 problem - please help

[Hal0XSn1p3r]

Extra Info -

I have recently sent my xbox away for repair due to RROD
They sent me back a new unit because they could not repair mine
So I go out and buy Fifa 09
Within a few games, it freezes
I thought it might just be a minor problem, so I took no notice of it
Then, it was perfect for about 3 days
But on Friday night, it froze again, repeatedely
I thought it had to be a faulty disc, because I play Halo 3 also and that was fine
So my I took it back to Gamestation today and they swapped it for a new copy
In the new disc goes
It freezes
In the exact same place it was freezing on friday night
(On the arena)
It can't be the disc because its brand new
And my unit is brand new
So what's the problem?
I will be very annoyed if I have to send my xbox off to Germany again and wait for another 2 weeks
Please, if you've got any ideas,
I would be very grateful