Thanks so much for your question. It sounds like your grandson is calling out for help. At 11 he's old enough to open up and provide some insight into why he's disobeying. Has there been a big change in his life recently--a divorce, a new school, the end of a friendship? He may be struggling with an issue that requires more than punishment. If he doesn't care about being grounded, he may be sad and depressed about something. Family counseling may be useful for getting at the heart of the matter and the family dynamics involved.
Your grandson is also old enough to understand that mutual respect is needed within a family. A "you scratch my back, I'll scratch yours" rule prevails. If he's not following the house rules, mom and dad are not motivated to do what he wants--driving him to his friend's house, taking him to the movies, or providing him with a cell phone. These are all perks he earns when he's a contributing member of the family unit.
Pointing out when he's doing helpful things will also make a big difference in his behavior. When kids are caught doing things well (cleaning their rooms, taking their dishes to the sink), it motivates them to continue.