What is Dad doing while his son is copping an attitude ? Sometimes the best way to solve the problem is to have his dad let him know in NO uncertain terms that NO ONE talks to his wife that way.
When our older girls were young teens, my husband didn't intervene if we argued, but when the kids got rude, he let them know they weren't allowed to talk to me that way.
the other thing I always did was to say that feelings are okay, but if you are going to behave inappropriately, you have to behave that way in your own room. When you are willing to behave politely, you may come out. I know he has to get ready for school, but if he's going to be loud, send him outdoors. He can bellow all he wants outside, and then come in and be quieter so the baby can sleep.
If the baby is up, I wouldn't worry about it. The infant will get used to the people in his environment.
Also watch for the source of the loudness and attitude -- is it because he isn't getting any attention because there's a newborn ? maybe you need to make some changes, too.
Personally, I have NEVER grounded my kids. And I never will. I don't think it's viable for discipline unlesss you are punishing them for staying out too late, or something like that. Making them stay home for acting out at home isn't helping you out much. It just makes both of you feel worse.