The flaps sounds should be audibile only when the engine is not running. This is actually a feature. To get more informations about how to operate the flaps without hearing them, please read this post: http://www.simcoders.com/2015/10/18/all-you-want-to-know-about-reps-flaps-implementation/
All you want to know about REP’s flaps implementation
In the last months many of you wrote an email to ask why with REP the flaps motor sound is not audible when the engine is on. That’s actually a feature. Le’ts see how you can use it to improve your pilot skills.