More than likely, this is nothing to worry about. Most radios do this. But just to be on the safe side, make sure that the control surfaces that the servos are attached to are not binding. If they are, the servos could be trying to return to neutral but are having a bit of a struggle because they have to push/pull too hard against the control surface. Disconnect each pushrod from the servo (Sometimes it's easier just to unscrew the servo arm) and move the control surface through it's full range to ensure there is no binding. A servo fighting against binding will draw more power and quickly flattening your battery pack resulting in a crash. If there is binding, find the cause and fix it. You will be thankful you did.