I recently had my car serviced. A few days later, it wouldn’t start. We called AAA, they said it was the battery. They replaced it. But now my radio won’t work and the car is making a low humming noise, from the engine area. Is there more I need to look into regarding the charging system to make sure I don’t have something other than a bad battery going on?

You did not tell us want make model and year car you have, but most newer cars have a security system for the radio that may cause this kind of reaction. It is there to make the radio less attractive to someone trying to steal it.

Your owner’s manual should address this issue. There likely will be a code that you need to input to reactivate the radio. That code may be in the manual, or somewhere hidden in the car or trunk or it may be lost. The dealer may be able to rest, or find the original code or may know of a way to get around it. So might many of our readers, but without knowing what car you have, they will not know if the have the right answer.

Whatever is hummimg is also probably draining the battery. You may need further repair work done.