There should not be any additional requirements when specifying custom .wav
files. Please use the files from the folder [RadControlls for ASP.NET AJAX install folder]\App_Data\RadCaptcha
, replace them with yours to check if the problem is related to the RadCaptcha control or the quality of your custom files and let me know how it goes.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed