Radio/tape Cd Player problems of the 2007 BMW 530

I'm an owner of the Bmw530i & around the end of April I began to feel a jerk type of motion (a slight acceleration) when I came to a stop . I called the dealer who asked if they could test drive it because they cannot explain what that could be . On 5/30/2013 I took the car into the dealer & I was told the car may just need to be updated because they could not explain what was causing the jerking motion upon stopping . After about 1 hr 1/2 I was told they needed me to give them authorization to push pass there system because for some unknown reason there system keeps stopping/unable to diagnose & the tech says they tried several times & if they continued it could possibly blow my electrical or radio system , they would not take the responsibility . I could not take that chance because that is the only vehicle my self & family has . So at that point the tech & the service mgr explained that there was nothing else they could do & they felt it was still a safe vehicle to drive . BMW should be able to diagnose there own vehicles & is this a manufacturers defect ? I am very disappointed & concerned about the safety & security of my self & my children .