MARIAH CAR­EY and Nick Cannon’s mar­riage appears to have hit a rough patch after stories began swirling that BOTH stars have been flirting a lit­tle too much say sources.

On Sept. 12, Mariah, 44, was spotted having fun with rapper Nas at his 40th birth­day party. Sporting a sexy black dress and a sparkly sling on her right arm, eyewitness­es noticed that the “Always Be My Baby” singer was NOT wear­ing her wedding ring.

According to one published report, the two were whispering and giggling all night. The singer was also said to be very touchy-feely with the rapper.

A representa­tive for Carey denied that there is trouble in the marriage, and Mariah even tweeted a photo of her boobs to Nick as a sexy treat for his birthday on Oc­tober 8.

But sources say it wasn’t the first time in recent months that Mariah’s been seen with­out her sparkler – prompting Hollywood in­siders to ask: Are the couple covering up secrets that could lead to a $500 million divorce battle?

Reports in June placed a ringless Mariah in an Atlanta recording studio with rapper Young Jeezy. Carey collabo­rated with Jeezy on the song Side Effects prior to her 2008 marriage to Cannon.

And she didn’t appear to be wearing her ring back on

June 2 when she took the stage with sexy singer Miguel to perform their duet, “#Beautiful,” at a concert in New Jersey.

As The ENQUIRER previously re­ported, Nick, 33, was also jealous over the long hours Mariah spent helping pal Arsenio Hall plan the launch of his recently debuted talk show.

“All of this cavorting around with handsome men has Nick seeing red,” the source continued. “He’s about at the end of his rope with Mariah.”

But Mariah isn’t the only one fac­ing allegations about being overly flirtatious. As we reported in 2011, she feared that her much-younger hubby was trying to hook up with a sexy, young “AGT” competitor.

At the time, sources said she was “feeling insecure” about the excess baby weight she was carrying after the April 2011 birth of the couple’s twins, Monroe and Moroccan, as well as about Nick’s pre-marriage reputation as a womanizer.

She was “almost beside herself with worry that Nick would stray,” revealed an insider. “I think she fears Nick’s wandering eye – once a cheater, always a cheater – and she zeroed in on his infatuation with” the AGT competitor.

More recently, on Aug. 20, Mariah surprised Nick during an episode of his MTV2 show, Wild ’N Out. She walked onstage while he was flirting with one of the show’s con­testants and threatened to “shut all this (bleep) down” before he cut to a commercial break.

“Things have just gone from bad to worse for them,” added the source, although Mariah’s sexy tweet may put matters on a differ­ent path.”