"I hum a little," she told the December/January issue of Ladies' Home Journal. "When your husband's a huge singer, the last thing you do is sing with him."
But while they may not sing together, the couple is all about communicating.
"Keith and I have a very honest, profound marriage, which we both contribute to every day," she said. "We have a phrase, 'Does this contribute to the good of our union?' Because that's what's most important."
And Nicole said she is still mad over her man, whom she married in 2006.
"I love being in love. I believe in the power of love, the way it can heal. The more you keep choosing it — because there are times when you can choose to be angry at the person or to love him — the more it nourishes a family," she said.
The actress, who made almost 20 films between 2001 and 2008, said she's now putting family first.
"I was running from my life, in a way," she said. "My imaginary life was better than my flesh-and-blood life. That's a sad thing to say, but it was. Now I love my real life so much it requires an enormous belief in a film to want to take it on.
"I think that we're in the world to connect. Because that's what you're left with. You're not left with your houses or awards or money, you're left with the people that you built relationships with," she added.
Nicole said she was thrilled their family grew with the addition of baby Sunday Rose, who was born last year.
"I loved bringing life into the world. To be completely responsible for this baby growing inside me, I'm grateful for that experience," she said.
But having the baby also helped Nicole fill out her red carpet dresses a bit more.
"They're not very big, my boobs, so they just became normal size. I loved it! I felt very 'Woman,' she said. "When you've had a slightly androgynous body your whole life, having breasts is a nice feeling."