They may appear like the perfect rock 'n' roll couple, but a source tells X17online exclusively that Gwen Stefani and Gavin Rossdale are anything but -- and that Gwen's been trashing him in songs written for the new No Doubt album!

Gwen's been busy writing and recording with her multi-platinum, uber-successful group, but Gavin hasn't been happy about the tone her songs have taken.

    "A lot of the new songs are about Gavin and what a jerk he is," says our source. "They're so negative, he finally had to tell her 'No more songs about me!'"

Gwen always wrote about her relationships in the past, with the bittersweet ballads "Don't Speak" and "Cool" about ex Tony Kanal, and even though she's expressed her feelings towards Gavin in song before (with "Ex-Girlfriend" and "Simple Kind of Life"), this is far worse than anything we've heard previously, says our source.

"Gwen was pissed that Courtney Love recently blabbed about her affair with Gavin. Gwen knew they had been together, but not right before their wedding," says the insider. "Some of the songs call him out for being a cheater!"

But even though their marriage isn't picture-perfect, our source says that Gwen still wants to expand their family. "Gwen is 40 and desperate to have another child," says the spy, who tells us Gwen and everyone around her are totally mum on whether she will become a mom again.