What are the rights I have when it comes to a bondsman harassing me about something my grandson did?

If you signed on the grandson's bond, then they can come after you if he violates the bond. If by "harass" you mean they demand payment, they can do that. And, they can sue you. If you are not on his bond and there is no reason for them to contact you, then you can report them to the local bail bond board.