Sources tell ABC11 the investigation centers around allegations the officers had sex with a known prostitute.
The same sources tell ABC11 the officers are Sgt. Rick J. Armstrong, Chris L. Hill, Mike C. Rominski, and Stephen D. Hinnant.
The Raleigh Police Department has not publically named the men who were all assigned to the Field Operations Division.
A police spokesman said Hinnant has resigned from the department. He would not say if any of the other men have been placed on administrative duty citing privacy laws.
Police Chief Harry Dolan told ABC11 Tuesday that the investigation was launched in late 2009, after an officer in the department filed a complaint with Internal Affairs.
In a statement, Chief Dolan said the "complaint concerned the possibility of improper conduct on the part of certain RPD police officers."
The statement went on to say that a comprehensive investigation found "that administrative violations may have occurred and that they stemmed from voluntary interactions between a small number of officers" and individuals outside of the department.
Sources tell ABC11 the department used GPS units as well as cameras during the investigation to track the officers and link them to the woman.
ABC11 is not naming her because she may be considered a victim in the case.
The Raleigh Police Department is treating the case as a personnel matter and has not said what will happen to the officers. The Wake County District Attorney says criminal charges are not likely to be filed.