MY BMW x5 2006 is having problems turning over?

it started a month or so ago and would only start on the second try, as soon as it started running it was fine. the engine sounds great after it turns over. recently i noticed it does it alot more. now i cant go a day without it hesitating on me. we JUST had the oil changed and have always kept maintenance up on it. the only thing i can think of is before my husband left for afghanistan he installed a bass system in it, could that be draining the battery? we just bought the car not 6 months ago, and have had ongoing problems with the dealership, im hoping this isnt another thing i can contribute to their shadiness. also yesterday the system stabilization control lamp was lit??? im so confused!! help!