There's also the possibility they're into S&M, though if that were the case the smart option would have been for the wife to clarify things when you approached her--rather than telling you to fuck off. The last thing someone in that situation wants is for the cops to bust down their door in the middle of their "fun", especially given how hard it can be to explain. That being said, people aren't always smart.
Did you hear what sounded like an argument, or just the sounds of someone being hit/crying out? If it sounded like an actual fight, calling the cops is probably a good idea.