Had the same issue a while ago. It was caused by my battery going dead and sending varying voltage to the car. I also found a thread that said to reset the BAS but I forget how exactly that was done. I think it was something like "Crank the engine and center your steering wheel then turn your steering as far to the left till it stops as possible then as far to the right as possible then back to the middle position, turn the car off".
But you guys might check the search function and it's also in the manual I believe!